Electrophotographic organophotoreceptors with novel charge transport compounds

ABSTRACT

Charge transport compounds are described that have a multiple number of hydrazone-bridged heterocyclic groups (especially julolidine, carbazole and/or triarylmethane groups) connected by a central bridging group. An example of charge transport compounds are those having the following generic formula: 
     
       
         (R—Q)n-Y  Formula I 
       
     
     wherein R is selected from the group consisting of julolidine ring groups, carbazole ring groups, and triarylmethane ring groups; 
     Q comprises an aromatic hydrazone linking group, such as                    
     Y comprises a bridging group between R—Q— groups, such as a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a methylene group; Z is an aryl group, preferably a phenyl group or naphthyl group; X is a linking group, preferably amethylene group, and for example having the formula —(CH 2 ) m -(branched or linear), where m is an integer between 0 and 20, inclusive, and one or more of the methylene groups is optionally replaced by an oxygen atom, a carbonyl group, urethane, urea, an ester group, a —NR 6  group, a CHR 7  group, or a CR 8 R 9  group where R 6 , R 7 , R 8 , and R 9  are, independently, H, an alkyl group, or aryl group; and n is an integer between 2 and 6, inclusive. An organic photoreceptor includes that compound and (b) a charge generating compound; and (c) an electrically conductive substrate.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to organophotoreceptors suitable for use inelectrophotography and, more specifically, to flexibleorganophotoreceptors having novel charge transport compounds.

Background of the Art

In electrophotography, an organophotoreceptor in the form of a plate,disk, sheet, belt, or drum having an electrically insulatingphotoconductive element on an electrically conductive substrate isimaged by first uniformly electrostatically charging the surface of thephotoconductive layer, and then exposing the charged surface to apattern of light. The light exposure selectively dissipates the chargein the illuminated areas, thereby forming a pattern of charged anduncharged areas. A liquid or solid toner is then deposited in either thecharged or uncharged areas to create a toned image on the surface of thephotoconductive layer. The resulting visible toner image can betransferred to a suitable receiving surface such as paper. The imagingprocess can be repeated many times.

Both single layer and multilayer photoconductive elements have beenused. In the single layer embodiment, a charge transport material andcharge generating material are combined with a polymeric binder and thendeposited on the electrically conductive substrate. In the multilayerembodiment, the charge transport material and charge generating materialare in the form of separate layers, each of which can optionally becombined with a polymeric binder, deposited on the electricallyconductive substrate. Two arrangements are possible. In one arrangement(the “dual layer” arrangement), the charge generating layer is depositedon the electrically conductive substrate and the charge transport layeris deposited on top of the charge generating layer. In an alternatearrangement (the “inverted dual layer” arrangement), the order of thecharge transport layer and charge generating layer is reversed.

In both the single and multilayer photoconductive elements, the purposeof the charge generating material is to generate charge carriers (i.e.,holes or electrons) upon exposure to light. The purpose of the chargetransport material is to accept these charge carriers and transport themthrough the charge transport layer in order to discharge a surfacecharge on the photoconductive element.

To produce high quality images, particularly after multiple cycles, itis desirable for the charge transport material to form a homogeneoussolution with the polymeric binder and remain in solution. In addition,it is desirable to maximize the amount of charge which the chargetransport material can accept (indicated by a parameter known as theacceptance voltage or “V_(acc)”), and to minimize retention of thatcharge upon discharge (indicated by a parameter known as the residualvoltage or “V_(res)”).

There are many charge transport materials available forelectrophotography. The most common charge transport materials arepyrazoline derivatives, fluorene derivatives, oxadiazole derivatives,stilbene derivatives, hydrazone derivatives, carbazole hydrazonederivatives, polyvinyl carbazole, polyvinyl pyrene, orpolyacenaphthylene. However, each of the above charge transportmaterials suffer some disadvantages. There is always a need for novelcharge transport materials to meet the various requirements ofelectrophotography applications.

SUMMARY OF THE INVENTION

A charge transport compound having the following generic formula:

(R—Q)n-Y  Formula I

wherein R is a heterocyclic group, preferably a heterocyclic groupselected from the group consisting of julolidine ring groups, carbazolering groups, and triarylmethane ring groups (examples of otherheterocyclic groups being the following non-limiting list of such asthiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline,imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine,imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole,naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g.,2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole,indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine,pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole,tetrazole, urazole, carbazole, julolidine, or thiadiazole ring.);

Q comprises an aromatic hydrazone linking group, such as

Y comprises a bridging group between R—Q— groups, such as a bond, carbonatom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear—(CH₂)p— group where p is an integer between 0 and 10, an aryl group, acycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxylgroup), a heterocyclic group, or a CR₁₀ group where R₁₀ is hydrogenatom, an alkyl group, or aryl group;

Z is an aryl group, preferably a phenyl group or naphthyl group;

X is a linking group, preferably a methylene group, and for examplehaving the formula —(CH₂)_(m)— (branched or linear), where m is aninteger between 0 and 20, inclusive, and one or more of the methylenegroups is optionally replaced by an oxygen atom, a carbonyl group,urethane, urea, an ester group, a —NR₆ group, a CHR₇ group, or a CR₈R₉group where R₆, R₇, R₈, and R₉ are, independently, H, an alkyl group, oraryl group; and

n is an integer between 2 and 6, inclusive.

In another aspect of the invention, the invention features an organicphotoreceptor that includes:

(a) a charge transport compound having the formula

(R—Q)n-Y  Formula I

wherein R is a heterocyclic group, preferably a heterocyclic groupselected from the group consisting of julolidine ring groups, carbazolering groups, and triarylmethane ring groups (examples of otherheterocyclic groups being the following non-limiting list of such asthiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline,imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine,imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole,naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g.,2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole,indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine,pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole,tetrazole, urazole, carbazole, julolidine, or thiadiazole ring.);

Q comprises an aromatic hydrazone linking group, such as

Y comprises a bridging group, preferably a divalent linking group,between R—Q— groups, such as a bond, carbon atom, nitrogen atom, oxygenatom, sulfur atom, a branched or linear —(CH₂)_(p)— group where p is aninteger between 0 and 10, an aryl group, a cycloalkyl group, acyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclicgroup, or a CR₁₀ group where R₁₀ is hydrogen atom, an alkyl group, oraryl group;

Z is an aryl group, preferably a phenyl group or naphthyl group;

X is a linking group, preferably a methylene group, and for examplehaving the formula —(CH₂)_(m)— (branched or linear), where m is aninteger between 0 and 20, inclusive, and one or more of the methylenegroups is optionally replaced by an oxygen atom, a carbonyl group,urethane, urea, an ester group, a —NR₆ group, a CHR₇ group, or a CR₈R₉group where R₆, R₇, R₈, and R₉ are, independently, H, an alkyl group, oraryl group; and

n is an integer between 2 and 6, inclusive;

(b) a charge generating compound; and

(c) an electrically conductive substrate.

DETAILED DESCRIPTION OF THE INVENTION

A charge transport compound having the following generic formula:

(R—Q)n-Y  Formula I

wherein R is a heterocyclic group, preferably a heterocyclic groupselected from the group consisting of julolidine ring groups, carbazolering groups, and triarylmethane ring groups (examples of otherheterocyclic groups being the following non-limiting list of such asthiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline,imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine,imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole,naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g.,2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole,indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine,pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole,tetrazole, urazole, carbazole, julolidine, or thiadiazole ring.);

Q comprises an aromatic hydrazone linking group, such as

Y comprises a bridging group between R—Q— groups, such as a bond, carbonatom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear—(CH₂)_(p)— group where p is an integer between 0 and 10, an aryl group,a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxylgroup), a heterocyclic group, or a CR₁₀ group where R₁₀ is hydrogenatom, an alkyl group, or aryl group;

Z is an aryl group, preferably a phenyl group or naphthyl group;

X is a linking group, preferably a methylene group, and for examplehaving the formula —(CH₂)_(m)— (branched or linear), where m is aninteger between 0 and 20, inclusive, and one or more of the methylenegroups is optionally replaced by an oxygen atom, a carbonyl group,urethane, urea, an ester group, a —NR₆ group, a CHR₇ group, or a CR₈R₉group where R₆, R₇, R₈, and R₉ are, independently, H, an alkyl group, oraryl group; and

n is an integer between 2 and 6, inclusive.

Various specific classes of charge transport compound within the scopeof Formula I include, but are not limited to the following:

In a first aspect, the invention features an organophotoreceptor thatincludes:

(a) a charge transport compound having the formula

where n is an integer between 2 and 6, inclusive;

R₁, R₂, R₃, and R₄ are, independently, hydrogen, a halogen atom, hydroxygroup, thiol group, an alkoxy group, a branched or linear alkyl group(e.g., a C₁-C₂₀ alkyl group), a branched or linear unsaturatedhydrocarbon group, an ether group, nitro group, an amino group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group); and

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 50, inclusive, and one or more ofthe methylene groups is optionally replaced by a bond, an oxygen atom, asulfur atom, a carbonyl group, an urethane group, an urea group, anester group, an aryl group, a cycloalkyl group, a cyclosiloxyl group(e.g., a cyclotetrasiloxyl group), a heterocyclic group, a NR₅ group, aCHR₆ group, or a CR₇R₈ group where R₅, R₆, R₇, and R₈ are,independently, H, an alkyl group, or an aryl group.

The charge transport compound may or may not be symmetrical. Thus, forexample, a linking group X for any given “arm” of the compound may bethe same or different from the linking groups in other “arms” of thecompound. Similarly, the R₁, R₂, R₃, and R₄ groups for any given “arm”of the compound may be the same or different from the R₁, R₂, R₃, and R₄groups in any other arm. In addition, the above-described formula forthe charge transport compound is intended to cover isomers; or

b) a charge transport compound of the formula:

where n is an integer between 2 and 6, inclusive;

R₁ is hydrogen, a branched or linear alkyl group (e.g., a C₁-C₂₀ alkylgroup), a branched or linear unsaturated hydrocarbon group, an ethergroup, or an aryl group (e.g., a phenyl or naphthyl group);

R₂ is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group,a branched or linear alkyl group (e.g., a C₁-C₂₀ alkyl group), abranched or linear unsaturated hydrocarbon group, an ether group, acycloalkyl group (e.g. a cyclohexyl group), an aryl group (e.g., aphenyl or naphthyl group), or a —NR₄R₅ group where R₄ and R₅ are,independently, hydrogen, a branched or linear alkyl group, a branched orlinear unsaturated hydrocarbon group, a cycloalkyl group, an aryl group,or R₄ and R₅ combine with the nitrogen atom to form a ring;

R₃ is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group,a branched or linear alkyl group (e.g., a C₁-C₂₀ alkyl group), abranched or linear unsaturated hydrocarbon group, an ether group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group);

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 20, inclusive, and one or more ofthe methylene groups is optionally replaced by an oxygen atom, acarbonyl group, urethane, urea, an ester group, a —NR₆ group, a CHR₇group, or a CR₈ R₉ group where R₆, R₇, R₈, and R₉ are, independently, H,an alkyl group, or aryl group; and

Y is a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, abranched or linear —(CH₂)_(p)— group where p is an integer between 0 and10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., acyclotetrasiloxyl group), a heterocyclic group, or a CR₁₀ group whereR₁₀ is hydrogen atom, an alkyl group, or aryl group;

(b) a charge generating compound; and

(c) an electrically conductive substrate.

The charge transport compound may or may not be symmetrical. Thus, forexample, a linking group X for any given “arm” of the compound may bethe same or different from the linking groups in other “arms” of thecompound. Similarly, the R₁, R₂, and R₃ groups for any given “arm” ofthe compound may be the same or different from the R₁, R₂, and R₃ groupsin any other arm. In addition, the above-described formula for thecharge transport compound is intended to cover isomers.

The organic photoreceptor may be provided in the form of a flexiblebelt. In one embodiment, the organic photoreceptor includes: (a) acharge transport layer comprising the charge transport compound and apolymeric binder; (b) a charge generating layer comprising the chargegenerating compound and a polymeric binder; and (c) the electricallyconductive substrate. The charge transport layer may be intermediate thecharge generating layer and the electrically conductive substrate.Alternatively, the charge generating layer may be intermediate thecharge transport layer and the electrically conductive substrate.

The invention also features the charge transport compounds themselves.In one preferred embodiment, a charge transport compound is selected inwhich n is 2, Y is a bond or a —CH₂— group, X has the formula —CH₂)_(m)—where m is an integer between 2 and 5, inclusive, and R₁ is an ethyl,heptyl, or —(CH₂)₃C₆H₅ group. Specific examples of suitable chargetransport compounds have the following formulae:

In one preferred embodiment, a charge transport compound is selected inwhich n is 2, X is a (CH₂)_(m) group where m is an integer between 2 and20, and R₁, R₂, R₃, and R₄ are hydrogen. Specific examples of suitablecharge transport compound have the following general formula where m isan integer between 2 and 20; more preferably m is an integer between 4and 10; most preferably m is 5, as in Compound (11).

In a second aspect, the invention features an electrophotographicimaging apparatus that includes (a) a plurality of support rollers, atleast one having a diameter no greater than about 40 mm; and (b) theabove-described organic photoreceptor in the form of a flexible beltthreaded around the support rollers. The apparatus preferably furtherincludes a liquid toner dispenser.

In a third aspect, the invention features an electrophotographic imagingprocess that includes (a) applying an electrical charge to a surface ofthe above-described organic photoreceptor; (b) imagewise exposing thesurface of the organic photoreceptor to radiation to dissipate charge inselected areas and thereby form a pattern of charged and uncharged areason the surface; (c) contacting the surface with a liquid toner thatincludes a dispersion of colorant particles in an organic liquid tocreate a toned image; and (d) transferring the toned image to asubstrate.

In a fourth aspect, the invention features a novel charge transportmaterial having the formula

where n is an integer between 2 and 6, inclusive;

R₁ is hydrogen, a branched or linear alkyl group (e.g., a C₁-C₂₀ alkylgroup), a branched or linear unsaturated hydrocarbon group, an ethergroup, or an aryl group (e.g., a phenyl or naphthyl group);

R₂ is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group,a branched or linear alkyl group (e.g., a C₁-C₂₀ alkyl group), abranched or linear unsaturated hydrocarbon group, an ether group, acycloalkyl group (e.g. a cyclohexyl group), an aryl group (e.g., aphenyl or naphthyl group), or a —NR₄R₅ group where R₄ and R₅ are,independently, hydrogen, a branched or linear alkyl group, a branched orlinear unsaturated hydrocarbon group, a cycloalkyl group, an aryl group,or R₄ and R₅ combine with the nitrogen atom to form a ring;

R₃ is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group,a branched or linear alkyl group (e.g., a C₁-C₂₀ alkyl group), abranched or linear unsaturated hydrocarbon group, an ether group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group);

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 20, inclusive, and one or more ofthe methylene groups is optionally replaced by an oxygen atom, acarbonyl group, urethane, urea, an ester group, a —NR₆ group, a CHR₇group, or a CR₈R₉ group where R₆, R₇, R₈, and R₉ are, independently, H,an alkyl group, or aryl group; and

Y is a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, abranched or linear —(CH₂)_(p)— group where p is an integer between 0 and10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., acyclotetrasiloxyl group), a heterocyclic group, or a CR₁₀ group whereR₁₀ is hydrogen atom, an alkyl group, or aryl group.

Mixed (e.g., at least two Q groups are selected from two differentclasses selected from the group consisting of julolidine, carbazole, andtriarylmethane) may be represented by the following various subgenericformulae:

Specific subgeneric examples of charge transport compound according toformula (IV) have the following general formula (V) where m is aninteger between 2 and 20; more preferably m is an integer between 4 and10.

Another example of such a mixed charge transport compound has theformula (VI):

where R₁ is hydrogen, a branched or linear alkyl group (e.g., a C₁-C₂₀alkyl group), a branched or linear unsaturated hydrocarbon group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group);

R₂, R₃, R₄, R₅, and R₆ are, independently, hydrogen, a halogen atom,hydroxy group, thiol group, an alkoxy group, a branched or linear alkylgroup (e.g., a C₁-C₂₀ alkyl group), a branched or linear unsaturatedhydrocarbon group, an ether group, nitro group, an amino group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group); and

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 50, inclusive, and one or more ofthe methylene (CH₂) groups is optionally replaced by oxygen atom, sulfuratom, a carbonyl group, an urethane group, an urea group, an estergroup, an aryl group, a heterocyclic group, a cycloalkyl group, acyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a cycloalkylgroup, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a NR₇group, a CHR₈ group, or a CR₈R₁₀ group where R₇, R₈, R₉, and R₁₀, are,independently, H, an alkyl group, or an aryl group.

In one specific embodiment of structural Formula VI, a charge transportcompound is selected in which X is a —CH₂)_(m)— group where m is aninteger between 2 and 20, R₁ is an alkyl group, and R₂, R₃, R₄, R₅ andR₆ are hydrogen. Specific examples of suitable charge transport compoundhave the following general formula where m is an integer between 2 and20; more preferably m is an integer between 4 and 10.

and Formula (IX) wherein:

the subgeneric formula below applies:

where R₁ is hydrogen, a branched or linear alkyl group (e.g., a C₁-C₂₀alkyl group), a branched or linear unsaturated hydrocarbon group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group);

R₂, R₃, R₄, R₅, and R₆ are, independently, hydrogen, a halogen atom,hydroxy group, thiol group, an alkoxy group, a branched or linear alkylgroup (e.g., a C₁-C₂₀ alkyl group), a branched or linear unsaturatedhydrocarbon group, an ether group, nitro group, an amino group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group); and

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 50, inclusive, and one or more ofthe methylene (CH₂) groups is optionally replaced by oxygen atom, sulfuratom, a carbonyl group, an urethane group, an urea group, an estergroup, an aryl group, a heterocyclic group, a cycloalkyl group, acyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a NR₇ group, aCHR₈ group, or a CR₉R₁₀ group where R₇, R₈, R₉, and R₁₀, are,independently, H, an alkyl group, or an aryl group.

Another generic formula (IX) is directed to charge transport compoundshaving the formula

wherein R₁ and R₂ are, independently, hydrogen, a halogen atom, hydroxygroup, thiol group, an alkoxy group, a branched or linear alkyl group(e.g., a C₁-C₂₀ alkyl group), a branched or linear unsaturatedhydrocarbon group, an ether group, nitro group, an amino group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group);

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 50, inclusive, and one or more ofthe methylene groups is optionally replaced by a bond, an oxygen atom, asulfur atom, a carbonyl group, an urethane group, an urea group, anester group, an aryl group, a heterocyclic group, a NR₄ group, a CHR₅group, or a CR₆ R₇ group where R₄, R₅, R₆, and R₇ are, independently, H,an alkyl group, or an aryl group; and

Y and Z are, independently, a carbazole group, a triphenylamine group, ajulolidine group, or any of their derivatives.

The charge transport compound may have more than two arms such that thelinking group X may be linked to more than two hydrazone groups. Thecharge transport compound may or may not be symmetrical. Thus, forexample, a portion of the linking group X attached to any given “arm” ofthe compound may be the same or different from the remaining portion ofthe linking groups attached to other “arms” of the compound. Similarly,the R₁ and R₂ groups may be the same or different and the Y and Z groupsmay be the same or different. In addition, the above-described formulafor the charge transport compound is intended to cover isomers.

Another subgeneric formula (XI) for this class of charge transportcompound with only triarylmethane Q substituents has the formula

where n is an integer between 2 and 6, inclusive;

R₁, R₂, and R₃ are, independently, hydrogen, a halogen atom, hydroxygroup, thiol group, an alkoxy group, a branched or linear alkyl group(e.g., a C₁-C₂₀ alkyl group), a branched or linear unsaturatedhydrocarbon group, an ether group, nitro group, an amino group, acycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., aphenyl or naphthyl group); and

X is a linking group having the formula —(CH₂)_(m)—, branched or linear,where m is an integer between 0 and 50, inclusive, and one or more ofthe methylene groups is optionally replaced by a bond, an oxygen atom, asulfur atom, a carbonyl group, an urethane group, an urea group, anester group, an aryl group, a heterocyclic group, a NR₄ group, a CHR₅group, or a CR₆R₇ group where R₄, R₅, R₆, and R₇ are, independently, H,an alkyl group, or an aryl group. Specific and subgeneric centralnucleus examples of this formula (XI) are represented by:

Another aspect of the invention is the formation of charge transportcompounds with at least three hydrazone moieties or groups attached tothe bridging group. These compounds are represented by the generalformula, falling within generic Formula I, of a charge transportcompound having the formula:

R₁, R₂, and R₃ are, independently, a branched or linear alkyl group(e.g., a C₁-C₂₀ alkyl group), a branched or linear unsaturatedhydrocarbon group, a cycloalkyl group (e.g. a cyclohexyl group), aheterocyclic group, or an aryl group (e.g., a phenyl or naphthyl group);

R₄, R₅, and R₆ are, independently, triarylamine (e.g., triphenylamine),diaryl alkylamine, dialkyl arylamine, a carbocyclic ring such asanthraquinone, diphenoquinone, indane, or fluorenone, or a heterocyclicring such as thiazoline, thiazolidine, phenothiazine, oxazoline,imidazoline, imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone,morpholine, imidazole, benzothiazole, benzotriazole, benzoxazole,benzimidazole, naphthothiazole, naphthoxazole, naphthimidazole,quinoline (e.g., 2-quinoline or 4-quinoline), isoquinoline, quinoxaline,indole, indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine,pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole,tetrazole, urazole, carbazole, julolidine, or thiadiazole ring. Theseheterocyclic rings may also have substituents such as halogen atoms(e.g., chlorine, bromine and fluorine), alkyls (e.g., methyl, ethyl,n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, t-octyl, octyl,octadecyl, etc.), alkoxys (e.g., methoxy, ethoxy, butoxy, etc.), aryls(e.g., phenyl, tolyl, xylyl, etc.), aryloxys (e.g., phenoxy,methylphenoxy, chlorophenoxy, dimethylphenoxy, etc.), N-substitutedaminos (e.g., N-methylamino, N-ethylamino, N-t-butylamino, N-octylamino,N-benzylamino, acetylamino, benzoylamino, etc.), N,N-disubstitutedaminos (e.g., N,N-dimethylamino, N,N-diethylamino, N,N-dipropylamino,N,N-di-t-butylamino, N,N-dibenzylamino, N-ethyl-N-benzylamino, etc.),acyls (e.g., acetyl, propionyl, benzoyl, methylbenzoyl, dimethylbenzoyl,chlorobenzoyl, etc.), carbamoyl, sulfamoyl, nitro, cyano, hydroxy,carboxy, sulfonate, oxo, benzo, naptho, indeno, and phosphate; and

X is a linking group having the formula

where m, n, and o is an integer between 0 and 50, inclusive; one or moreof the methylene groups is optionally replaced by a bond, an oxygenatom, a sulfur atom, a carbonyl group, an urethane group, an urea group,an ester group, an aryl group, a heterocyclic group, a NR₅ group, a CHR₆group, or a CR₇R₈ group where R₅, R₆, R₇, and R₈ are, independently, H,an alkyl group, or an aryl group; and the C-H group is optionallyreplaced by a nitrogen atom, a boron atom, a metal atom, and a CR₉ groupwhere R₉ is an alkyl group or an aryl group.

A photoconductor system exits with a combination of a) and (b) a chargegenerating compound; and (c) an electrically conductive substrate.

The charge transport compound may have more than three arms such thatthe linking group X may be linked to more than three hydrazone groups.The charge transport compound may or may not be symmetrical. Thus, forexample, a portion of the linking group X attached to any given “arm” ofthe compound may be the same or different from the remaining portion ofthe linking groups attached to other “arms” of the compound. Similarly,the R₁, R₂, and R₃ groups may be the same or different and the R₄, R₅,and R₆ groups may be the same or different. In addition, theabove-described formula for the charge transport compound is intended tocover isomers.

The organophotoreceptor may be provided in the form of a plate, a disc,a flexible belt, a rigid drum, or a sheet around a rigid or compliantdrum. In one embodiment, the organophotoreceptor includes: (a) a chargetransport layer comprising the charge transport compound and a polymericbinder; (b) a charge generating layer comprising the charge generatingcompound and a polymeric binder; and (c) the electrically conductivesubstrate. The charge transport layer may be intermediate between thecharge generating layer and the electrically conductive substrate.Alternatively, the charge generating layer may be intermediate betweenthe charge transport layer and the electrically conductive substrate.

In describing chemicals by structural formulae and group definitions,certain terms are used in a nomenclature format that is chemicallyacceptable. The terms groups, central nucleus, and moiety have definedmeanings. The term group indicates that the generically recited chemicalmaterial (e.g., alkyl group, phenyl group, carbazole group, etc.) mayhave any substituent thereon which is consistent with the bond structureof that group. For example, alkyl group includes alkyl materials such asmethyl ethyl, propyl iso-octyl, dodecyl and the like, and also includessuch substituted alkyls such as chloromethyl, dibromoethyl,1,3-dicyanopropyl, 1,3,5-trihydroxyhexyl, 1,3,5-trifluorocyclohexyl,1-methoxy-dodecyl, and the like. However, as is consistent with suchnomenclature, no substitution would be included within the term thatwould alter the fundamental bond structure of the underlying group. Forexample, where a pheny ring group or central nucleus of a phenyl groupis recited, substitution such as 1-hydroxyphenyl, 2,4-fluorophenyl,orthocyanophenyl, 1,3,5-trimethoxyphenyl and the like would beacceotable within the terminology, while substitution of1,1,2,2,3,3-hexamethylphenyl would not be acceptable as thatsubstitution would require the ring bond structure of the phenyl groupto be altered to a non-aromatic form because of the substitution.Similarly, where the term a “central nucleus of the formula” is used anda structural formula is shown, any substituent may be provided on thatformula, as long as the substutution does not alter the underlying bondstructure of the formula (e.g., by require a double bond to be convertedto a single bond, or opening a ring group, or dropping a describedsubstituent group in the formula). Where the term moirty is used, suchas alkyl moiety or phenyl moiety, that terminology indicates that thechemical material is not substituted.

In a second aspect, the invention features an electrophotographicimaging apparatus that includes (a) a plurality of support rollers; and(b) the above-described organophotoreceptor in the form of a flexiblebelt threaded around the support rollers. The apparatus preferablyfurther includes a liquid toner dispenser.

In a third aspect, the invention features an electrophotographic imagingprocess that includes (a) applying an electrical charge to a surface ofthe above-described organophotoreceptor; (b) imagewise exposing thesurface of the organophotoreceptor to radiation to dissipate charge inselected areas and thereby form a pattern of charged and uncharged areason the surface; (c) contacting the surface with a liquid toner thatincludes a dispersion of colorant particles in an organic liquid tocreate a toned image; and (d) transferring the toned image to asubstrate.

In a fourth aspect, the invention features a novel charge transportmaterial having the formula

R₁, R₂, and R₃ are, independently, described above;

R₄, R₅, and R₆ are, independently, as described above;

X is a linking group having the formula

where m, n, and o are as described above.

Specific examples of suitable charge transport compounds have thefollowing formulae:

The charge transport compounds according to Formulae (I)-(XIII) may beprepared by a multi-step synthesis using a combination of knownsynthetic techniques.

The first step is the preparation of one or more of aldehyde derivativeof any heterocyclic compound, preferably carbazole, triphenylamine, orjulolidine (heterocyclic group, preferably a heterocyclic group selectedfrom the group consisting of julolidine ring groups, carbazole ringgroups, and triarylmethane ring groups (examples of other heterocyclicgroups being the following non-limiting list of such as thiazoline,thiazolidine, phenothiazine, oxazoline, imidazoline, imidazolidine,thiazole, oxazole, isoxazole, oxazolidinone, morpholine, imidazole,benzothiazole, benzotriazole, benzoxazole, benzimidazole,naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g.,2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole,indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine,pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole,tetrazole, urazole, carbazole, julolidine, or thiadiazole ring) byVilsmeier reaction between carbazole, triphenylamine, or julolidinecorrespondingly and phosphorus oxychloride (POCl₃). Carbazole,triphenylamine, or julolidine is dissolved in N,N-dimethylformamide(DMF) and then the solution is cooled. Then POCl₃ (10-15% excess) isadded slowly via a dropping funnel to the cooled DMF solution.

The second step is the reaction between phenylhydrazine and one of thealdehyde derivative of carbazole, triphenylamine, or julolidine in amolar ratio of 1:1 to form the corresponding hydrazone derivative byrefluxing the reactants in THF for two hours. More than one hydrazonederivative may be prepared if an unsymmetrical charge transport compoundis desired.

The last step is the reaction of one of the hydrazone with adibromoalkane in a molar ratio of 2:1 to form a symmetrical chargetransport compound. The hydrazone obtained is dissolved in DMSO. Afterthe addition of 25% aqueous solution of NaOH, a dibromoalkane is addedto the solution. This solution is stirred at 70° C. for approximately 1hour. The product from this reaction is purified by recrystallization.If an unsymmetrical charge transport compound is desired, two or moredifferent hydrazones are used. Each hydrazone will react, one at a time,with a dibromoalkane or an alkane with more than two bromo groups in amolar ratio of 1:1 under condition described above.

Formula 12 may be prepared by the condensation reaction of4-(diphenylamino)-benzaldehyde with phenyl hydrazine; and then by anucleophilic substitution reaction of the product of the condensationreaction with a dibromoalkane to form the final dimeric charge transportmaterial. Specifically, Compound 13 may be prepared according to theabove synthesis wherein the dibromoalkane is 1,5-dibromopentane.

The invention provides novel charge transport materials for organicphotoreceptors featuring a combination of good mechanical andelectrostatic properties. These photoreceptors can be used successfullywith liquid toners to produce high quality images. The high quality ofthe images is maintained after repeated cycling.

Other features and advantages of the invention will be apparent from thefollowing description of the preferred embodiments thereof, and from theclaims.

The invention features organic photoreceptors that include chargetransport compounds having the formulae set forth in the Summary of theInvention above. The charge transport compounds according to Formula (1)may be prepared by a multi-step synthesis using a combination of knownsynthetic techniques. For example, the general synthetic method forsynthesis of Compounds 5-7 was according to a 4-step syntheticprocedure. The first step is N-alkylatation of carbazole to introduce analkyl group to the carbazole nitrogen. The second step is the formationof a —CHO group on the carbazole ring by Vilsmeier reaction. The thirdstep is the formation of hydrazone by the reaction of the product fromstep 2 with a hydrazine. The last step is a nucleophilic substitutionreaction to form a bridging group between two or more hydrazonemoieties. Compounds 2-4 were prepared according to the above procedureexcept the first and second steps were skipped because the startingmaterials for step three are commercially available.

The organophotoreceptor may be in the form of a plate, drum, or belt,with flexible belts being preferred. The organophotoreceptor may includean electrically conductive substrate and a photoconductive element inthe form of a single layer that includes both the charge transportcompound and charge generating compound in a polymeric binder.Preferably, however, the organophotoreceptor includes an electricallyconductive substrate and a photoconductive element that is a bilayerconstruction featuring a charge generating layer and a separate chargetransport layer. The charge generating layer may be located intermediatethe electrically conductive substrate and the charge transport layer.Alternatively, the photoconductive element may be an invertedconstruction in which the charge transport layer is intermediate theelectrically conductive substrate and the charge generating layer.

The electrically conductive substrate may be flexible, for example inthe form of a flexible web or a belt, or inflexible, for example in theform of a drum. Typically, a flexible electrically conductive substratecomprises of an insulated substrate and a thin layer of electricallyconductive materials. The insulated substrate may be paper or a filmforming polymer such as polyethylene terepthalate, polyimide,polysulfone, polyethylene naphthalate, polypropylene, nylon, polyester,polycarbonate, polyvinyl fluoride, polystyrene and the like. Specificexamples of supporting substrates included polyethersulfone (StabarS-100, available from ICI), polyvinyl fluoride (Tedlar, available fromE.I. DuPont de Nemours & Company), polybisphenol-A polycarbonate(Makrofol, available from Mobay Chemical Company) and amorphouspolyethylene terephthalate (Melinar, available from ICI Americas, Inc.).The electrically conductive materials may be graphite, dispersed carbonblack, iodide, conductive polymers such as polypyroles and CalgonConductive polymer 261 (commercially available from Calgon Corporation,Inc., Pittsburgh, Pa.), metals such as aluminum, titanium, chromium,brass, gold, copper, palladium, nickel, or stainless steel, or metaloxide such as tin oxide or indium oxide. Preferably, the electricallyconductive material is aluminum. Typically, the photoconductor substratewill have a thickness adequate to provide the required mechanicalstability. For example, flexible web substrates generally have athickness from about 0.01 to about 1 mm, while drum substrates generallyhave a thickness of from about 0.5 mm to about 2 mm. Typical structuresfor polycarbonates include:

The charge generating compound is a material which is capable ofabsorbing light to generate charge carriers, such as a dyestuff orpigment. Examples of suitable charge generating compounds includemetal-free phthalocyanines (e.g., Progen 1 x-form metal-freephthalocyanine from Zeneca, Inc.), metal phthalocyanines such astitanium phthalocyanine, copper phthalocyanine, oxytitaniumphthalocyanine, hydroxygallium phthalocyanine, squarylium dyes andpigments, hydroxy-substituted squarylium pigments, perylimides,polynuclear quinones available from Allied Chemical Corporation underthe tradename Indofast Double Scarlet, Indofast Violet Lake B, IndofastBrilliant Scarlet and Indofast Orange, quinacridones available fromDuPont under the tradename Monastral Red, Monastral Violet and MonastralRed Y, naphthalene 1,4,5,8-tetracarboxylic acid derived pigmentsincluding the perinones, tetrabenzoporphyrins andtetranaphthaloporphyrins, indigo- and thioindigo dyes,benzothioxanthene-derivatives, perylene 3,4,9,10-tetracarboxylic acidderived pigments, polyazo-pigments including bisazo-, trisazo- andtetrakisazo-pigments, polymethine dyes, dyes containing quinazolinegroups, tertiary amines, amorphous selenium, selenium alloys such asselenium-tellurium, selenium-tellurium-arsenic and selenium-arsenic,cadmium sulphoselenide, cadmiumselenide, cadmium sulphide, and mixturesthereof. Preferably, the charge generating compound is oxytitaniumphthalocyanine, hydroxygallium phthalocyanine or a combination thereof.

Preferably, the charge generation layer comprises a binder in an amountof from about 10 to about 90 weight percent and more preferably in anamount of from about 20 to about 75 weight percent, based on the weightof the charge generation layer.

The binder is capable of dispersing or dissolving the charge transportcompound (in the case of the charge transport layer) and the chargegenerating compound (in the case of the charge generating layer).Examples of suitable binders for both the charge generating layer andcharge transport layer include polystyrene-co-butadiene, modifiedacrylic polymers, polyvinyl acetate, styrene-alkyd resins, soya-alkylresins, polyvinylchloride, polyvinylidene chloride, polyacrylonitrile,polycarbonates, polyacrylic acid, polyacrylates, polymethacrylates,styrene polymers, polyvinyl butyral, alkyd resins, polyamides,polyurethanes, polyesters, polysulfones, polyethers, polyketones,phenoxy resins, epoxy resins, silicone resins, polysiloxanes,poly(hydroxyether) resins, polyhydroxystyrene resins, novolak,poly(phenylglycidyl ether)-co-dicyclopentadiene, copolymers of monomersused in the above-mentioned polymers, and combinations thereof.Polycarbonate binders are particularly preferred. Examples of suitablepolycarbonate binders include polycarbonate A which is derived frombisphenol-A, polycarbonate Z, which is derived from cyclohexylidenebisphenol, polycarbonate C, which is derived from methylbisphenol A, andpolyestercarbonates.

The photoreceptor may include additional layers as well. Such layers arewell-known and include, for example, barrier layers, release layers,adhesive layer, and sub-layer. The release layer forms the uppermostlayer of the photoconductor element with the barrier layer sandwichedbetween the release layer and the photoconductive element. The adhesivelayer locates and improves the adhesion between the barrier layer andthe release layer. The sub-layer is a charge blocking layer and locatesbetween the electrically conductive substrate and the photoconductiveelement. The sub-layer may also improve the adhesion between theelectrically conductive substrate and the photoconductive element.

Suitable barrier layers include coatings such as crosslinkablesiloxanol-colloidal silica coating and hydroxylatedsilsesquioxane-colloidal silica coating, and organic binders such aspolyvinyl alcohol, methyl vinyl ether/maleic anhydride copolymer,casein, polyvinyl pyrrolidone, polyacrylic acid, gelatin, starch,polyurethanes, polyimides, polyesters, polyamides, polyvinyl acetate,polyvinyl chloride, polyvinylidene chloride, polycarbonates, polyninylbutyral, polyvinyl acetoacetal, polyvinyl formal, polyacrylonitrile,polymethyl methacrylate, polyacrylates, polyvinyl carbazoles, copolymersof monomers used in the above-mentioned polymers, vinyl chloride/vinylacetate/vinyl alcohol terpolymers, vinyl chloride/vinyl acetate/maleicacid terpolymers, ethylene/vinyl acetate copolymers, vinylchloride/vinylidene chloride copolymers, cellulose polymers, andmixtures thereof. The above organic binders optionally may contain smallinorganic particles such as fumed silica, silica, titania, alumina,zirconia, or a combination thereof. The typical particle size is in therange of 0.001 to 0.5 micrometers, preferably 0.005 micrometers. Apreferred barrier layer is a 1:1 mixture of methyl cellulose and methylvinyl ether/maleic anhydride copolymer with glyoxal as a crosslinker.

The release layer topcoat may comprise any release layer compositionknown in the art. Preferably, the release layer is a fluorinatedpolymer, siloxane polymer, fluorosilicone polymer, silane, polyethylene,polypropylene, or a combination thereof. More preferably, the releaselayers is crosslinked silicone polymers.

Typical adhesive layers include film forming polymers such as polyester,polyvinylbutyral, polyvinylpyrolidone, polyurethane, polymethylmethacrylate, poly(hydroxy amino ether) and the like. Preferably, theadhesive layer is poly(hydroxy amino ether). If such layers areutilized, they preferably have a dry thickness between about 0.01micrometer and about 5 micrometers.

Typical sub-layers include polyvinylbutyral, organosilanes, hydrolyzablesilanes, epoxy resins, polyesters, polyamides, polyurethanes, siliconesand the like. Preferably, the sub-layer has a dry thickness betweenabout 20 Angstroms and about 2,000 Angstroms.

The charge transport compounds, and photoreceptors including thesecompounds, are suitable for use in an imaging process with either dry orliquid toner development. Liquid toner development is generallypreferred because it offers the advantages of providing higherresolution images and requiring lower energy for image fixing comparedto dry toners. Examples of useful liquid toners are well-known. Theytypically include a colorant, a resin binder, a charge director, and acarrier liquid. A preferred resin to pigment ratio is 2:1 to 10:1, morepreferably 4:1 to 8:1. Typically, the colorant, resin, and the chargedirector form the toner particles.

The invention will now be described further by way of the followingexamples.

EXAMPLES

A. Synthesis

Charge transport compounds were synthesized as follows. The numberassociated with each compound refers to the number of the chemicalformula set forth in the Summary of the Invention above.

Compound (2)

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added9-ethyl-3-carbazolecarboxyaldehyde (1 mole, 223.28 g, obtainedcommercially from Aldrich Chemical Company) and tetrahydrofuran (600ml). Heating was applied to ensure that all solid entered into solution.Phenyl hydrazine (119 g, 1.1 mole, obtained commercially from AldrichChemical Company) was added and the mixture was refluxed for 2 hours.When TLC showed the total disappearance of the starting material and theformation of the product, the flask was allowed to cool to roomtemperature and the solvent was evaporated. The solid was filtered of,washed with 20 ml of ethanol and dried. A yellow solid was obtained (263g, 80% yield).

To a 250 ml 3-neck round bottom flask equipped with thermometer andmechanical stirrer were added the yellow solid (0.1 mole, 33.14 g)prepared above and DMSO (50 ml). After the solid was dissolved,1,10-Dibromodecane (15 g, 0.05 mole, obtained commercially from AldrichChemical Company) was added. An aqueous solution of 50% NaOH (20 g) wasadded and heated to 85° C. for 2 hours. The mixture was cooled to roomtemperature and then added to 2 L of water. A light yellow solid wasprecipitated out, filtered, washed with water, and dried. The yield was49 g (61%); m.p.=119° C. The ¹H-NMR spectrum of the solid shows peaks at1.26-1.52 ppm (m; 16H); 1.62-1.84 ppm (m; 4H); 3.82-4.01 ppm (t; 4H);4.25-4.47 ppm (q, 6H); 6.85-6.96 ppm (t; 2H); 7.09-7.25 ppm (m; 2H);7.29-7.54 ppm (m; 12H); 7.70-7.79 ppm (s; 2H); 7.86-7.98 ppm (dd; 2H);8.08-8.19 ppm (d; 2H); 8.28-8.38 ppm (d; 2H). The H-NMR spectrum is infull agreement with the structure of Compound (2).

Compound (3)

Compound (3) was prepared according to the procedure of compound (2)except that 1,10-Dibromodecane (0.05 mole) was replaced with1,5-Dibromodecane (0.05 mole, obtained commercially from AldrichChemical Company). The yield was 65%; m.p.=203° C. The ¹H-NMR spectrumof the solid shows peaks at 1.35-1.49 ppm (t; 6H); 1.60-1.75 ppm (m;2H);1.77-1.97 ppm (m; 4H); 3.93-4.10 ppm (t; 4H); 4.28-4.44 ppm (q; 4H);6.86-6.98 ppm (t; 2H); 7.28-7.53 ppm (m; 14H); 7.73-7.82 ppm (s; 2H);7.88-7.99 ppm (dd; 2H); 8.06-8.17 ppm (d; 2H); 8.28-8.39 ppm (d, 2H).The ¹H-NMR spectrum is in full agreement with the structure of Compound(3).

Compound (4)

Compound (4) was prepared according to the procedure of compound (2)except that 1,10-Dibromodecane (0.05 mole) was replaced with1,4-Dibromodecane (0.05 mole, obtained commercially from AldrichChemical Company). The yield was 70%; m.p.=207° C. The ¹H-NMR spectrumof the solid shows peaks at 1.33-1.50 ppm (t; 6H); 1.80-2.06 ppm (m;4H); 3.92-4.16 ppm (m; 4H); 4.21-4.51 ppm (q=4H); 6.87-7.03 ppm (t=2H);7.10-7.24 ppm (m; 2H); 7.27-7.60 ppm (m; 14H); 7.72-7.82 ppm (s; 2H);7.87-7.98 ppm (dd; 2H); 8.04-8.19 ppm (d; 2H); 8.27-8.39 ppm (s; 2H).The ¹H-NMR spectrum is in full agreement with the structure of Compound(4).

Compound (5)

To a 3-liter 3-neck round bottom flask equipped with a reflux condenserand a mechanical stirrer were added carbazole (177.78 g, 1.063 mole,obtained commercially from Aldrich Chemical Company), 1-bromoheptane(200 g, 1.117 mole, obtained commercially from Aldrich ChemicalCompany), and toluene (800 ml). The mixture was stirred at roomtemperature for 30 minutes. Then the mixture was refluxed for 5 hoursafter 50% NaOH aqueous solution (400 g) was added. The mixture wascooled to room temperature and an organic phase appeared. The organicphase was separated, washed with water, dried over Mg₂SO₄, filtered, andevaporated to remove all solvent. An oil was obtained. The yield was 78%(220 g). A ¹H-NMR spectrum was recorded and it was in agreement with thestructure of N-heptylcarbazole.

To a 1-liter 3-neck round bottom flask equipped with a mechanicalstirrer, a dropping funnel, and a thermometer were addedN-heptylcarbazole (282 g, 1.062 mole, prepared in the previous step) andDMF (500 ml). The flask was placed on ice bath until temperature insideis 5° C., then POCl₃ (109 g, 1.17 mole) was added dropwise via thedropping funnel. During the addition the temperature was not allowed torise above 5° C. After the addition was completed, the flask was placedin a boiling water bath for 2 hours. Then the solution in the flask wascooled to room temperature and added to a large volume of water (3liter). The solid was filtered off, washed repeatedly with water, anddried. The yield was 75%. A ¹H-NMR spectrum was recorded and it was inagreement with 9-heptylcarbazole-3-carboxyaldehyde.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added9-heptylcarbazole-3-carboxyaldehyde (1 mole, 293.45 g) and 600 ml oftetrahydrofuran. Heating was applied to ensure that all solid enteredinto solution. Phenyl hydrazine (119 g, 1.1 mole, obtained commerciallyfrom Aldrich Chemical Company) was added and the mixture was refluxedfor 2 hours. When TLC showed the total disappearance of the startingmaterial and the formation of the product, the flask was allowed to coolto room temperature and the solvent was evaporated. The solid wasfiltered of, washed with 20 ml of ethanol and dried. A yellow solid wasobtained (249 g, 83% yield).

To a 250 ml 3-neck round bottom flask equipped with thermometer andmechanical stirrer were added the yellow solid (0.1 mole, 38.36 g)prepared above and 50 ml of DMSO. After the solid was dissolved,1,10-Dibromodecane (15 g, 0.05 mole) was added. An aqueous solution of50% NaOH (20 g) was added and heated to 85° C. for 2 hours. The mixturewas cooled to room temperature and then added to 2 L of water. A lightyellow solid was precipitated out, filtered, washed with water, anddried. The yield was 25 g (55%); m.p.=116° C. The ¹H-NMR spectrum of thesolid shows peaks at 0.70-0.96 ppm (t; 6H); 1.01-1.62 ppm (m; 28H);1.64-2.00 ppm (m; 8H); 3.80-4.06 ppm (t; 4H); 4.18-4.42 ppm (t; 4H);6.67-7.00 ppm (t; 2H); 7.12-7.29 ppm (m; 4H); 7.28-7.58 ppm (m; 12H);7.67-7.81 ppm(s; 2H); 7.85-8.01 ppm (dd; 2H); 8.07-8.22 ppm (d; 2H);8.26-8.43 ppm (s; 2H). The ¹H-NMR spectrum is in full agreement with thestructure of Compound (5).

Compound(6)

Compound (6) was prepared according to the procedure of compound (5)except that 1,10-Dibromodecane was replaced with 1,5-Dibromodecane. Theyield was 45%, m.p.=120° C. The ¹H-NMR spectrum of the solid shows peaksat 0.69-0.95 ppm (t; 6H); 1.05-1.49 ppm (m; 20H); 1.75-1.98 ppm (m; 6H);3.84-4.12 ppm (t; 4H); 4.16-4.40 ppm (t; 4H); 6.86-7.00 ppm (t; 2H);7.15-7.29 ppm (m; 4H); 7.37-7.51 ppm (m; 12H); 7.71-7.83 ppm (s; 2H);7.88-8.00 ppm (dd; 2H); 8.06-8.19 ppm (d; 2H); 8.26-8.40 ppm (s, 2H).The ¹H-NMR spectrum is in full agreement with the structure of Compound(6).

Compound (7)

Compound (7) was prepared according to the procedure of compound (5)except that 1-bromoheptane was replaced with 1-bromo-3-propylbenzene.The yield was 60%, m.p.=184° C. The ¹H-NMR spectrum is in full agreementwith the structure of Compound (6).

B. ¹H NMR Measurements

The ¹H-NMR spectra were obtained by a 300 MHz Bruker NMR spectrometer(obtained commercially from Bruker Instruments Inc., Billerica, Mass.)using CDCl₃ solvent with 0.03% v/v tetramethylsialine (obtainedcommercially from Aldrich Chemical Company) as the internal reference.The following abbreviations were used: s=singlet; d=doublet; dd=doubledoublet; m=multiplet; q=quartet; and t=triplet.

C. Thermal Transitions

Thermal transition data for various charge transport materials wascollected using a TA Instruments Model 2929 Differential ScanningCalorimeter (New Castle, DE) equipped with a DSC refrigerated coolingsystem (−70° C. minimum temperature limit), and dry helium and nitrogenexchange gases. The calorimeter ran on a Thermal Analyst 2100workstation with version 8.10B software. An empty aluminum pall was usedas the reference.

Samples were tested both neat and as a mixture with Polycarbonate Z(“IPCZ”). The neat samples were prepared by placing 4.0 to 8.0 mg ofneat charge transport material into an aluminum sample pan and crimpingthe upper lid to produce a hermetically sealed sample for DSC testing.The results were normalized on a per mass basis.

The Polycarbonate Z-mixed samples were prepared by filling the bottomportion of the aluminum sample pan to capacity with a 15-20% solidssolution of the charge transport material in Polycarbonate Z, followedby air-drying overnight. Each air-dried sample was then placed in aconvection oven at 50-55° C. for another 24-48 hours to eliminate tracesolvent, after which the upper sample lid was crimped on to produce ahermetically sealed sample for DSC testing. Typical sample size was 7.0to 15.0 mg. Again, the results were normalized on a per mass basis.

Each sample was subjected to the following protocol to evaluate itsthermal transition behavior:

1. Equilibrate at 0° C. (Default—Nitrogen Heat Exchange Gas);

2. Isothermal for 5 min.;

3. External Event: Nitrogen Heat Exchange Gas;

4. Ramp 10.0° C./min. to a temperature 30° C. above the melting point ofthe charge transport material;

5. External Event: Helium Heat Exchange Gas;

6. Isothermal for 5 min.;

7. Ramp 10.0° C./min. to 0° C.;

8. External Event: Nitrogen Heat Exchange Gas;

9. Isothermal for 5 min.;

10. Ramp 10.0° C./min. to a temperature 40° C. above the melting pointof the charge transport material;

11. External Event: Helium Heat Exchange Gas;

12. Isothermal for 5 min.;

13. Ramp 10.0° C./min. to 0° C.;

14. External Event: Nitrogen Heat Exchange Gas;

15. Isothermal for 5 min.;

16. Ramp 10.0° C./min. to 275° C.

The first cycle (steps 1-7) was used to (a) remove the thermal historyof the sample, (b) obtain the melting transition for crystalline chargetransport materials, and (c) obtain a homogeneous charge transportmaterial/Polycarbonate Z mixture in the event the charge transportmaterial crystallized during sample preparation. A homogeneous mixtureis obtained only if the charge transport material (melt or cast) ismiscible with the Polycarbonate-Z.

The second cycle (steps 8-13) was used to identify the glass transitiontemperature and charge transport material recrystallization or meltingtransitions.

The third cycle (steps 14-16) was used to report the final thermaltransitions.

The results are shown below in Table 1. All temperatures are reported in° C. “CTM” refers to the charge transport compound. “PCZ” refers toPolycarbonate Z binder.

TABLE 1 Tg with 50% PCZ Compund M.p (° C.) Tg without binder (° C.) (°C.) 2 119 46 83.7 3 203 84.4 102.5 4 207 79.1 NA 5 116 29.3 56.9 6 12044.5 78.3 7 184 57.4 NA

As expected, an increase in the aliphatic chain length of R₁ (inFormula 1) from ethyl to heptyl lowers the Tg (Compare Compound (2) withCompound (5)). Also, an increase in the chain length of the X—Y linkage(in Formula 1) from pentyl to decyl also lowers the Tg (CompareCompounds (2) with (3)). In the presence of Polycarbonate Z binder, theTg of Compounds (4) and (7) could not be measured due to phaseseparation.

D. Organic Photoreceptor Preparation Methods

(i) Die Coating

A charge transport solution containing 50 wt. % of a selected chargetransport compound in Polycarbonate Z binder (obtained commercially fromMitsubishi Gas Chemical under the designation “Lupilon Z-200” resin) wasprepared by combining a solution of either 10.0 g or 15.0 g, dependingupon solubility, of the charge transport compound in 120.0 g oftetrahydrofuran with 15.0 g of Polycarbonate Z and 0.03 g of Dow Corning510 Fluid. The charge transport solution was then die coated onto 3 mil(76 micrometer) thick polyethylene terephthalate (PET) film (Melinex 442polyester film from Dupont) having a 1 ohm/square aluminum vapor coatand an additional 0.25 micrometer thick PET sub-layer overlaying thealuminum vapor coat. The purpose of including the PET sub-layer was toimprove adhesion and prevent charge injection into the charge transportlayer. The dried charge transport layer had a nominal thickness of 8.75micrometers. Die coating (also known as slot coating) techniques aredescribed by E. Cohen and E. Gutoff, Modern Coating and DryingTechnology, VCH Publishers, Inc. New York, 1992, pp. 117-120.

A dispersion was prepared by micronising 32.6 g of oxytitaniumphthalocyanine pigment (obtained commercially from H. W. Sands Corp.,Jupiter, Fla.), 32.6 g of S-Lec B Bx-5 polyvinyl butyral resin (obtainedcommercially from Sekisui Chemical Co. Ltd.), and 684.4 g of 2/1 (v/v)methyl ethyl ketone/toluene using a horizontal sand mill operating inrecirculation mode for 8 hours. This stock solution was diluted to 3.5wt. % solids by adding 1113 g of 2:1 (v/v) methyl ethyl ketone/tolueneprior to coating. The resulting dispersion was die coated onto thecharge transport layer and dried to form a charge generating layerhaving a nominal thickness of 0.27 micrometer. This dual layer organicphotoconductor was then overcoated with a barrier layer.

Two different barrier layer solutions were used. The first (“Barrier A”)was prepared by mixing 86.3 g of 3% Methocel A15L V in water, 86.3 g of3% Gantrez AN-169 polymer (obtained commercially from ISP Technologies)in water, 172.44 g of methanol, 0.65 g of 40% Glyoxal 40 in water, and0.07 g Triton X-100 surfactant. The other barrier layer solution(“Barrier B”) was prepared by combining 217.6 g of 6% S-Lec Bx-5polyvinyl butyral resin, 1385.7 g isopropyl alcohol, 33.5 g Nalco 1057colloidal silica, 33.1% Z-6040 silane (Dow Coming 50/50 in isopropylalcohol/water), and 130.17 g Gantrez AN-169 polymer following theprocedure described in U.S. Pat. No. 5,733,698.

The barrier layer solution was die coated onto the dual layer organicphotoconductor and dried to form a layer having a nominal thickness of0.4 micrometer.

ii. Lamination

Inverted dual layer organophotoreceptors were prepared incorporatingcompounds 2-7 as charge transport material. A charge transport solutioncontaining 50 wt. % of a selected charge transport compound inPolycarbonate Z binder was prepared by combining a solution of 1.25 g ofthe charge transport compound in 8.0 g of tetrahydrofuran with 1.25 g ofPolycarbonate Z in 2.50 g of toluene. The charge transport solution wasthen hand-coated with a Maier rod (# 36) onto a 3 mil (76 micrometer)thick aluminized polyethylene terephthalate film (Melinex 442 polyesterfilm from Dupont having a 1 ohm/square aluminum vapor coat) having a 0.3micron polyester resin sub-layer (Vitel PE-2200 from Bostik, Middletown,Mass.) and dried to form a charge transport layer having a thickness of9 micrometers.

A dispersion was prepared by micronising 1.35 g of oxytitaniumphthalocyanine pigment (H. W. Sands Corp., Jupiter, Fla.), 1.35 g ofS-Lec B Bx-5 polyvinylbutryal resin (Sekisui Chemical Co. Ltd.), 26 g ofmethyl ethyl ketone, and 13 g of toluene using a horizontal sand milloperating in recirculation mode for 8 hours. The resulting dispersionwas then die coated onto unsubbed 2 mil (51 micrometer) thickpolyethylene terephthalate (PET) film and dried at 80° C. for 10 minutesto form a charge generating layer having a thickness of 0.27 micrometeron the PET film.

The charge transport layer and the charge generating layer werelaminated together at 140° C. using a Model 447 Matchprint TM Laminator(obtained commercially from Imation Corp., Oakdale, Minn.). Afterlamination, the 2 mil (51 micrometer) PET film was peeled off thesurface of the charge generation layer to form the inverted dual layerorganophotoreceptor.

E. Solubility Testing

Solubility testing of each individual charge transport compound wasperformed at room temperature using tetrahydrofuran as the solvent.Solubility results were reported as the percent solids of saturatedsolution. In general, it is desirable to maximize the solubility value.

F. Electrostatic Testing

Electrostatic testing was performed on a number of inverted dual layerorganic photoreceptor samples. The samples were prepared either bylamination or by die coating.

Electrostatic testing of compounds 2-7 was performed and recorded on aQEA PDT-2000 instrument at ambient temperature. Charge-up was performedat 8 kV. Discharge was performed by exposing the photoreceptor to a 780nm-filtered tungsten light source down a fiber optic cable. Each samplewas exposed to 2 microjoules/cm² of energy for 0.05 seconds; the totalexposure intensity was 20 microwatts/cm². After charge-up, theacceptance voltage (V_(acc)) was measured in volts. This value wasrecorded as V_(acc) after one cycle. Following this initial charge-up, aone second dark decay followed before the sample was discharged with the0.05 second light pulse of 2 microjules/cm² at 780 nm, after which theresidual voltage (V_(res)) was measured in volts. This value wasrecorded as V_(res) after one cycle. V_(acc) and V_(res) were alsomeasured after a total of 1000 cycles. In general, it is desirable tomaximize V_(acc) and to minimize V_(res).

TABLE 2 Compound V_(acc) (V) Dark Decay (V) Discharge (V) V_(res) (V) 2575 64 398 58 3 512 109 393 50 5 596 38 89 468 6 560 151 322 91

The data in Table 2 indicate that these charge transport materials aresuitable for making photoreceptors.

Examples 8-10

Compound (8)

To a 5-liter 3-neck round bottom flask equipped with a reflux condenser,mechanical stirrer and heating mantle were added carbazole (579.62 g,3.47 mole, obtained from Aldrich Chemical Company, Milwaukee, Wis.),1-bromo butane (500 g, 3.65 mole, obtained from Aldrich ChemicalCompany, Milwaukee, Wis.), benzyltriethylammonium chloride (39.48 g,0.17 mole, obtained from Aldrich Chemical Company, Milwaukee, Wis.), andtoluene (3 liter). The mixture was stirred at room temperature for 30minutes. Then 50% NaOH aqueous solution (1300 g) was added and themixture was refluxed for five hours. The mixture was cooled to roomtemperature and the organic phase was separated, washed with water anddried over magnesium sulfate, filtered, and evaporated to remove allsolvent. A liquid product was obtained. The yield was 644 g (83%). The¹H-NMR spectrum of the product in this step in CDCl₃ was in agreementwith the structure of N-butylcarbazole.

To a 3-liter, 3-neck round bottom flask equipped with a mechanicalstirrer, dropping funnel, and a thermometer were added N-butylcarbazole(644 g, 2.88 mole, prepared in the previous step) and DMF (1300 ml). Theflask was placed in ice bath until the temperature inside the flask is5° C., then POCl₃ (498 g, 3.25 mole, obtained from Aldrich ChemicalCompany) was added dropwise via the dropping funnel. During theaddition, the temperature was not allowed to rise above 5° C. Thesolution in the flask was cooled to room temperature and added to largevolume of water (3 Liter). The solid was filtered of, washed repeatedlywith water and dried. The yield was 668 g (92%). The ¹H-NMR spectrum ofthe product in this step in CDCl₃ was in full agreement with thestructure of 9-butylcarbazole-3-carboxaldyde.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added 9-butylcarbazole (668g, 2.66 mole, obtained from the previous step) and 500 ml of toluene,phenyl hydrazine (316.4 g, 2.93 mole, obtained from Aldrich ChemicalCompany). The mixture was refluxed for 2 hours. Thin layerchromatography (TLC) showed the total disappearance of the startingmaterial and the formation of the product. The flask was cooled to roomtemperature and the solid was collected, washed with 100 ml of ethanoland dried. The yield was 773 g (85%). The ¹H-NMR spectrum of the productin this step in CDCl₃ was in agreement with the expected product.

To a 250 ml 3-neck round bottom flask equipped with thermometer andmechanical stirrer were added the product from the previous step (34.15g, 0.1 mole) and 50 ml of DMSO. After the solid was dissolved,1,5-dibromoheptane (11.5 g, 0.05 mole, obtained from Aldrich ChemicalsCompany) was added. An aqueous solution of 50% NaOH (20 g) was added andthe mixture was heated to 85° C. for two hours. The mixture was cooledto room temperature and then added to 2L of water. A gummy solid wasformed which solidified upon standing at room temperature, which waswashed repeatedly with water and dried. A crude product (20 g) wasobtained. The product was recrystallized 4 times from ethyl acetate withactivated charcoal and silica. A light yellow solid was obtained whichwas dried in vacuum oven (80° C.) for six hours. The melting point wasfound to be 182-183° C. The ¹H-NMR of the final product in CDCl₃ showspeaks at 0.78-1.07 ppm (t; 6H); 1.31-1.49 ppm (m; 4H); 1.48-1.59 ppm (m,2H); 1.59-1.74 ppm (m; 2H); 1.75-1.99 ppm (m, 6H); 3.91-4.08 ppm (t;4H); 4.22-4.37 ppm (t; 4H); 6.79-7.03 ppm (t, 2H); 7.14-7.29 ppm (t;2H); 7.29-7.54 ppm (m; 14H); 7.71-7.85 ppm (s, 2H); 7.87-8.02 ppm (dd;2H); 8.05-8.21 ppm (d; 2H); 8.25-8.43 ppm (d; 2H). This ¹H-NMR spectrumis in agreement with the structure of compound (8).

Compound (9)

Compound (9) was prepared according to the procedure of compound (8)except that 1,5-dibromoheptane (0.05 mole) was replaced with 1,6-dibromohexane (0.05 mole, obtained from Aldrich Chemical Company). Themelting point was found to be 186-187° C. The ¹H-NMR spectrum of thefinal product in CDCl3 shows peaks at 0.84-1.05 ppm (t; 6H); 1.32-1.48ppm (m; 4H); 1.48-1.69 ppm (m; 4H); 1.73-1.99 ppm (m; 8H); 3.90-4.08 ppm(t; 4H); 4.21-4.40 ppm (t; 4H); 6.84-6.97 ppm (t; 2H); 7.15-7.25 ppm (t;2H); 7.29-7.56 ppm (m; 14H); 7.71-7.84 ppm (s; 2H); 7.84-7.99 ppm (dd;2H); 8.06-8.22 ppm (d; 2H); 8.26-8.43 ppm (d; 2H). The ¹H-NMR spectrumis in full agreement with structure (9).

Compound (10)

Compound (10) was prepared according to the procedure of compound (8)except that 1,5-dibromoheptane (0.05 mole) was replaced by1,8-dibromooctane (0.05 mole, obtained from Aldrich Chemical Company).The ¹H-NMR spectrum of the final product in CDCl₃ shows peaks at0.80-1.09 ppm (t; 6H); 1.19-1.98 ppm (m; 20 H); 3.85-4.07 ppm (t; 4H);4.17-4.40 ppm (t; 4H); 6.83-6.97 ppm (t; 2H); 7.13-7.56 ppm (m; 16 H);7.69-7.83 ppm (s; 2H); 7.85-7.99 ppm (dd; 2H); 8.05-8.20 ppm (d; 2H);8.25-8.41 ppm (d; 2H). The ¹H-NMR spectrum is in agreement with thestructure of compound (10).

G. Ionization Potential Protocol

Samples for ionization potential (Ip) measurements were prepared bydissolving Examples 2, 3, 5, 6, 8, 9, and Comparative Example Aindependently in tetrahydrofuran. Each solution was hand-coated on analuminized polyester substrate that was precision coated with amethylcellulose-based adhesion sub-layer to form a charge transfermaterial (CTM) layer. The role of this sub-layer was to improve adhesionof the CTM layer, to retard crystallization of CTM, and to eliminate theelectron photoemission from the Al layer through possible CTM layerdefects. No photoemission was detected from the Al through the sub-layerat illumination with up to 6.4 eV quanta energy light. In addition, theadhesion sub-layer was conductive enough to avoid charge accumulation onit during measurement. The thickness of both the sub-layer and CTM layerwas ˜0.4 μm. No binder material was used with CTM in the preparation ofthe samples for Ip measurements. In most cases, the thin CTM layers werein a meta-stabile amorphous phase, delaying crystallization for severalhours, so that measurement of the sample was possible. In some cases,however, crystallization began immediately after coating, as wasobserved with Compound 9. The sample layer of this CTM was amorphous butcrystal inclusions were present at the time of the Ip measurement.

The ionization potential was measured by the electron photoemission inair method similar to that described in “Ionization Potential of OrganicPigment Film by Atmospheric Photoelectron Emission Analysis”,Electrophotography, 28, Nr. 4, p. 364. (1989) by E. Miyamoto, Y.Yamaguchi, and M. Yokoyama, which is hereby incorporated by reference.The samples were illuminated with monochromatic light from the quartzmonochromator with a deuterium lamp source. The power of the incidentlight beam was 2-5·10⁻⁸ W. The negative voltage of −300 V was suppliedto the sample substrate. The counter-electrode with the 4.5×15 mm² slitfor illumination was placed at 8 mm distance from the sample surface.The counter-electrode was connected to the input of the BK2-16 typeelectrometer, working in the open impute regime, for the photocurrentmeasurement. A 10⁻¹⁵-10⁻¹² amp photocurrent was flowing in the circuitunder illumination. The photocurrent, I, was strongly dependent on theincident light photon energy hv. The I^(0.5)=f(hv) dependence wasplotted. Usually the dependence of the square root of photocurrent onincident light quanta energy is well described by linear relationshipnear the threshold [see references “Ionization Potential of OrganicPigment Film by Atmospheric Photoelectron Emission Analysis”,Electrophotography, 28, Nr. 4, p. 364. (1989) by E. Miyamoto, Y.Yamaguchi, and M. Yokoyama; and “Photoemission in Solids”, Topics inApplied Physics, 26, 1-103. (1978) by M. Cordona and L. Ley]. The linearpart of this dependence was extrapolated to the hv axis and Ip value wasdetermined as the photon energy at the interception point. Theionization potential measurement has an error of ±0.03 eV.

H. Hole Mobility

Samples for charge carrier mobility measurements were prepared bydissolving Examples 2, 3, 5, 6, 8, and Comparative Example Aindependently in tetrahydrofuran with a binder to form 10% solidsolutions. The binder was polycarbonate Z 200 (commercially obtainedfrom Mitsubishi Engineering Plastics, White Plains, N.Y.). Thesample/binder ratio was 4:6 or 5:5. Each solution was coated on analuminized polyester substrate to form a charge transfer material (CTM)layer. The thickness of the CTM layer varied in the range of 5-10 μm.The mobility for samples such as Compound 9 with limited solubilitycould not be measured.

The hole drift mobility was measured by a time of flight technique asdescribed in “The Discharge kinetics of negatively charged Seelectrophotographic layers,” Lithuanian Journal of Physics, 6, p.569-576 (1966) by E. Montrimas, V. Gaidelis, and A. Pa {tilde over(æ)}ra, which is hereby incorporated by reference. Positive coronacharging created electric field inside the CTM layer. The chargecarriers were generated at the layer surface by illumination with pulsesof nitrogen laser (pulse duration was 2 ns, wavelength 337 nm). Thelayer surface potential decreased as a result of pulse illumination wasup to 1-5% of initial potential before illumination. The capacitanceprobe that was connected to the wide frequency band electrometermeasured the speed of the surface potential dU/dt. The transit timet_(t) was determined by the change (kink) in the curve of the dU/dttransient in linear or double logarithmic scale. The drift mobility wascalculated by the formula μ=d²/U₀·t_(t), where d is the layer thicknessand U₀ is the surface potential at the moment of illumination.

Mobility values at electric field strength, E, of 6.4·10⁵ V/cm are givenin the Table 3. The mobility field dependencies may be approximated bythe function

μ˜e^(α{square root over (E)})

where α is parameter characterizing mobility field dependence. The valueof the parameter α is also given in Table 3.

TABLE 3 Hole mobility and ionization potential of charge transportmaterials Mobility μ, cm²/V · s Mobility Relative Compound Solubility at6.4 · 10⁵ V/cm to HCTM1 α Ip, eV 2 Sol. w/heat 40:60 5.44 3 Sol. w/heat1.1 × 10 − 5 at 40:60 with PC 1.22 5.34 5 Sol. w/o heat 1.7 × 10 − 5 at40:60 with PC 1.88 ˜0.006 5.38 6 Sol. w/o heat 6.5 × 10 − 6 at 40:60with PC 0.72 0.0053 5.23 8 Sol. w/o heat 3.6 × 10 − 6 at 40:60, 0.40˜0.007 5.4  5.6 × 10 − 6 at 50:50 with PC 0.62 0.009 9 Insoluble 5.35,layer with crystal inclusions Comparative 5.2 · 10⁻⁶ at 40:60 with PC0.58 ˜0.006 Example A*   9 · 10⁻⁶ at 50:50, 1.00 0.0055 5.23*Comparative Example A was Compound 2 in U.S. Pat. No. 6,140,004, whichis hereby incorporated by reference.

I. Extended Electrostatic Cycling

Extended electrostatic cycling was performed using an in-house designedand developed test bed that tests up to 3 samples strips that werewrapped around a drum. The three coated sample strips, each measuring 50cm long by 8.8 cm wide, were fastened side-by-side and completely aroundan aluminum drum (50.3 cm circumference). At least one of the strips wasa control sample (compound 11) that was precision web coated and used asan internal reference point. In this electrostatic cycling tester, thedrum rotated at a rate of 8.13 cm/min (3.2 ips) and the location of eachstation in the tester (distance and elapsed time per cycle) is given inTable 4:

TABLE 4 Electrostatic test stations around the sample sheet wrappeddrum. Total Distance, Total Time, Station Degrees cm sec Front erase baredge 0° Initial, 0 cm Initial, 0 s Erase Bar   0-7.2°   0-1.0   0-0.12Scorotron 113.1-135.3° 15.8-18.9 1.94-2.33 Laser Strike 161.0° 22.5 2.77Probe #1 181.1° 25.3 3.11 Probe #2 251.2° 35.1 4.32 Erase bar 360°  50.3 6.19

The first electrostatic probe (Trek 344 electrostatic meter,commercially obtained from Trek Inc., Medina, N.Y.) is located 0.34 safter the laser strike station and 0.78 s after the scorotron. Also, thesecond probe (Trek 344 electrostatic meter) is located 1.21 s from thefirst probe and 1.99 s from the scorotron. All measurements wereperformed at ambient temperature and relative humidity.

Electrostatic measurements were obtained as a compilation of severaltests. The first three diagnostic tests (prodstart, VlogE initial, darkdecay initial) are designed to evaluate the electrostatic cycling of anew, fresh sample and the last three, identical diagnostic tests(prodend, VlogE final, dark decay final) are run after cycling of thesample (longrun).

1) PRODSTART: The erase bar was turned on during this diagnostic testand the sample recharged at the beginning of each cycle (except whereindicated as scorotron off). The test sequence was as follows. Thesample was completely charged for three complete drum revolutions (laseroff); discharged with the laser @780 nm & 600 dpi on the forth cycle;completely charged for the next three cycles (laser off); dischargedwith only the erase lamp @720 nm on the eighth cycle (corona and laseroff); and, finally, completely charged for the last three cycles (laseroff).

2) VLOGE: This test measures the photoinduced discharge of thephotoconductor to various laser intensity levels by monitoring thedischarge voltage of the belt as a function of the laser power (exposureduration of 50 ns). The complete sample was charged and discharged atincremental laser power levels per each drum revolution. Asemi-logarithmic plot was generated (voltage verses log E) to identifythe sample's sensitivity and operational power settings.

3) DARK DECAY: This test measures the loss of charge acceptance withtime without laser or erase illumination and can be used as an indicatorof (i) the injection of residual holes from the charge generation layerto the charge transport layer, (ii) the thermal liberation of trappedcharges, and (iii) the injection of charge from the surface or aluminumground plane. After the belt has been completely charged, it was stoppedand the probes measured the surface voltage over a period of 90 seconds.The decay in the initial voltage was plotted verses time.

4) LONGRUN: The belt was electrostatically cycled for 100 drumrevolutions according to the following sequence per each belt-drumrevolution. The belt was charged by the corona, the laser was cycled onand off (80-100° sections) to discharge a portion of the belt and,finally, the erase lamp discharged the whole belt in preparation for thenext cycle. The laser was cycled so that the first section of the beltwas never exposed, the second section was always exposed, the thirdsection was never exposed, and the final section was always exposed.This pattern was repeated for a total of 100 drum revolutions and thedata for every 5^(th) cycle was recorded.

5) After the 100th cycle (long run test), the PRODSTART (now calledPRODEND), VLOGE, DARK DECAY diagnostic tests were run again.

Table 5 shows the results from the prodstart and prodend diagnostictests. The values for the charge acceptance voltage (V_(acc), probe #1average voltage obtained from the third cycle), discharge voltage (Vdis,probe #1 average voltage obtained from the fourth cycle), functionaldark decay voltage (Vdd, average voltage difference between probes 1 & 2obtained from the third cycle), and the residual voltage (Vres, averagevoltage obtained from the eighth cycle) are reported for the initial andfinal (post 100^(th) cycles) cycles.

TABLE 5 Electrostatic cycling of knife-coated inverted dual layerconstructions. Vacc, Vacc, Vdd, Vdd, Vdis, Vdis, Vres, Vres, Compoundintl final intl final intl final intl final 2 526 548 39 43 100 113 4357 3 495 509 44 44 67 73 22 31 5 639 686 54 46 545 612 434 488 6 546 56840 38 104 127 42 67 8 513 550 53 49 218 257 119 158 10  539 576 38 34161 203 77 123 Comparative 568 577 32 36 57 62 16 23 Example A*Comparative 500 525 17 26 73 81 22 30 Example A* *Comparative Example Awas Compound 2 in U.S. Pat. No. 6,140,004.

A. Synthesis

Compound (13) was synthesized as follows. To a 2-Liter 3-neck roundbottom flask, equipped with mechanical stirrer and reflux condenser,were added 112.0 g (0.41 mole) of 4-(Diphenylamino)benzaldehyde(commercially obtained from Aldrich, Milwaukee, Wis. and used asreceived) followed by the addition of 400 ml of THF. To this solution,were added, 48.77 g (0.45 mole) of phenylhydrazine (commerciallyobtained from Aldrich, Milwaukee, Wis. and used as received). Thesolution was refluxed for 2 hours. After cooled to room temperature, thesolvent was evaporated from the solution till the volume of the solutionwas 50 ml. Then a solid was precipitated by the addition of ethanol (50ml), collected by filtration, washed with ethanol (50 ml), and dried inoven vacuum for 6 hours at 60 C. The yield was 146 g (98%). The ¹H-NMRspectrum and IR spectrum of the solid in CDCl3 were in completeagreement with the expected product. The ¹H-NMR spectrum of the solidshows peaks at 3.8 ppm (N—H) (s; 1H) and 7.19-7.55 ppm (m; 20 H). The IRspectrum of the solid shows peaks at 1688 cm⁻¹ (C═O) and 3293 cm⁻¹(N—H).

To a 250 ml 3-neck round bottom flask, equipped with mechanical stirrerand thermometer, were added DMSO (100 ml) and the solid product (18.17g, 0.05 mole) from the reaction described above. The solution was heatedat 30 C. until the solid product entered into solution.1,5-Dibromopentane (5.75 g, 0.025 mole) (commercially obtained fromAldrich, Milwaukee, Wis.) was added to the solution and then 25% NaOHaqueous solution (20 g) was added. This solution was heated at 70-80 C.for 4 hours. After cooled to room temperature, a gummy material wasobserved in the bottom of the 3-neck round bottom flask. The liquidabove the gummy material was removed by decantation. The remaining gummymaterial was washed repeatedly with water to form a solid which then wasrecrystallized first from toluene/ethanol (50:50 by volume) withactivated charcoal. The material was recrystallized for the second andthird time from ethanol with activated charcoal and silica gel (addedonly in the third recrystallization). The product was dried at 50 C.oven vacuum for 6 hours. The yield was 7.90 g (40%). The melting pointwas found to be 77° C. The ¹H-NMR spectrum and the IR spectrum of theproduct in CDCl3 were in complete agreement with the proposed structure(3). The ¹H-NMR spectrum of the solid showed peaks at 1.51-1.59 ppm (m;2H); 1.73-1.81 ppm (t; 4H); 3.86-3.99 ppm (t; 4H); and 6.95-7.64 ppm (m;40H). The IR spectrum showed peaks at 2847 cm⁻¹, 2910 cm⁻¹, and 3031cm⁻¹.

B. ¹H NMR Measurements

The ¹H-NMR spectra were obtained by a 300 MHz Bruker NMR spectrometer(obtained commercially from Bruker Instruments Inc., Billerica, Mass.)using CDCl₃ solvent with 0.03% v/v tetramethylsialine (obtainedcommercially from Aldrich Chemical Company) as the internal reference.The following abbreviations were used: s=singlet; d=doublet; dd=doubledoublet; m=multiplet; q=quartet; and t=triplet.

C. IR Spectrum Measurements

The IR sample was obtained by placing a CH₂Cl₂ solution of the sample onan IR cards (3M disposable substrate type 61 polyethylene obtainedcommercially from 3M, St. Paul, Minn.). The IR spectrum was obtained bya Perkin Elmer 16 PC FT-IR Spectrometer obtained commercially fromPerkin Elmer, Norwalk, Conn.

D. Melting Point Measurement

Melting Point of Compound (12) was collected using a TA InstrumentsModel 2929 Differential Scanning Calorimeter (New Castle, Del.) equippedwith a DSC refrigerated cooling system (−70° C. minimum temperaturelimit), and dry helium and nitrogen exchange gases. The calorimeter ranon a Thermal Analyst 2100 workstation with version 8.10B software. Anempty aluminum pall was used as the reference.

The samples were prepared by placing 4.0 to 8.0 mg of Compound (3) intoan aluminum sample pan and crimping the upper lid to produce ahermetically sealed sample for DSC testing. The results were normalizedon a per mass basis.

Each sample was subjected to the following protocol to evaluate itsthermal transition behavior:

17. Equilibrate at 0° C. (Default—Nitrogen Heat Exchange Gas);

18. Isothermal for 5 min.;

19. External Event: Nitrogen Heat Exchange Gas;

20. Ramp 10.0° C./min. to a temperature 200° C.;

E. Organophotoreceptor Preparation Method

Inverted dual layer organophotoreceptors were prepared incorporatingCompound (12) and Comparative Example A (Formula (3) of U.S. Pat. No.6,066,426) obtained according to U.S. Pat. No. 6,066,426. A chargetransport solution containing 50 wt. % of Compound (3) in PolycarbonateZ binder was prepared by combining a solution of 1.25 g of Compound (3)in 8.0 g of tetrahydrofuran with 1.25 g of Polycarbonate Z in 2.50 g oftoluene. The charge transport solution was then hand-coated with a Maierrod (#40) onto a 76 micrometer (3 mil) thick aluminized polyethyleneterephthalate film (Melinex 442 polyester film from Dupont having a 1ohm/square aluminum vapor coat) having a 0.3 micron polyester resinsub-layer (Vitel PE-2200 from Bostik, Middletown, Mass.) and dried toform a charge transport layer having a thickness of 9 micrometers.

A dispersion was prepared by micronising 1.35 g of oxytitaniumphthalocyanine pigment (H. W. Sands Corp., Jupiter, Fla.), 1.35 g ofS-Lec B Bx-5 polyvinylbutryal resin (Sekisui Chemical Co. Ltd.), 26 g ofmethyl ethyl ketone, and 13 g of toluene using a horizontal sand milloperating in recirculation mode for 8 hours. The resulting dispersionwas then die coated onto unsubbed 2 mil (51 micrometer) thickpolyethylene terephthalate (PET) film and dried at 80° C. for 10 minutesto form a charge generating layer having a thickness of 0.27 micrometeron the PET film.

The charge transport layer and the charge generating layer werelaminated together at 140° C. using a Model 447 Matchprint TM Laminator(obtained commercially from Imation Corp., Oakdale, Minn.). Afterlamination, the 2 mil (51 micrometer) PET film was peeled off thesurface of the charge generation layer to form the inverted dual layerorganophotoreceptor.

F. Electrostatic Testing

Electrostatic testing was performed on a number of inverted dual layerorganophotoreceptor samples. The samples were prepared either bylamination or by die coating.

Electrostatic testing of Compound (12) and a control (structure wasperformed and recorded on a QEA PDT-2000 instrument at ambienttemperature. Charge-up was performed at 8 kV. Discharge was performed byexposing the photoreceptor to a 780 nm-filtered tungsten light sourcedown a fiber optic cable. Each sample was exposed to 2 microjoules/cm²of energy for 0.05 seconds; the total exposure intensity was 20microwatts/cm². After charge-up, the acceptance voltage (V_(acc)) wasmeasured in volts. This value was recorded as V_(acc) after one cycle.Following this initial charge-up, a one second dark decay followedbefore the sample was discharged with the 0.05 second light pulse of 2microjules/cm² at 780 nm, one second after which the decrease in voltage(Contrast) was measured in volts. Then the charge on the sample wasfurther reduced by an eraser lamp. The final residual voltage (V_(res))on the sample was measured in volts. V_(acc) and V_(res) were alsomeasured after a total of 1000 cycles. In general, it is desirable tomaximize V_(acc) and to minimize V_(res).

TABLE 1 Sample V_(acc) (V) Dark Decay (V) V_(res) (V) Contrast (V)Compound 3 363 142 18 195 Comparative 377 135 16 211 Example A

The data in Table 2 indicate that Compound (12) is suitable for makingphotoreceptors.

Compound (14)

The first step was the preparation of a 3-formyl-9-ethylcarbazole byVilsmeier reaction. 9-Ethylcarbazole (obtained commercially from AldrichChemical Company, Milwaukee, Wis.) was dissolved in dimethylformamide(DMF) and then the solution is cooled. Phosphorus oxychloride (POCl₃)(10-15% excess) is added slowly via a dropping funnel to the cooled DMFsolution. 3-Formyl-9-ethylcarbazole was isolated and purified.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added3-formyl-9-ethylcarbazole (1 mole, 223 g) and tetrahydrofuran (600 ml).Heating was applied to ensure that all solid entered into solution.Phenyl hydrazine (119 g, 1.1 mole, obtained commercially from AldrichChemical Company, Milwaukee, Wis.) was added and the mixture wasrefluxed for 2 hours. When TLC showed the total disappearance of thestarting material and the formation of the product, the flask wasallowed to cool to room temperature and the solvent was evaporated.3-Formyl-9-ethylcarbazole hydrazone was isolated and purified.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added4-(diphenylamino)benzaldehyde (1 mole, 273 g, commercially obtained fromFluke, Milwaukee, Wis.) and tetrahydrofuran (600 ml). Heating wasapplied to ensure that all solid entered into solution. Phenyl hydrazine(119 g, 1.1 mole, obtained commercially from Aldrich Chemical Company,Milwaukee, Wis.) was added and the mixture was refluxed for 2 hours.When TLC showed the total disappearance of the starting material and theformation of the product, the flask was allowed to cool to roomtemperature and the solvent was evaporated.4-(Diphenylamino)benzaldehyde hydrazone was isolated and purified.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added4-quinolinecarboxaldehyde (1 mole, 157.17 g, obtained commercially fromAldrich Chemical Company, Milwaukee, Wis.) and tetrahydrofuran (600 ml).Heating was applied to ensure that all solid entered into solution.Phenyl hydrazine (119 g, 1.1 mole, obtained commercially from AldrichChemical Company, Milwaukee, Wis.) was added and the mixture wasrefluxed for 2 hours. When TLC showed the total disappearance of thestarting material and the formation of the product, the flask wasallowed to cool to room temperature and the solvent was evaporated.4-Quinolinecarboxaldehyde hydrazone was isolated and purified.

The last step was the reaction of 3-formyl-9-ethylcarbazole hydrazone,4-(diphenylamino)benzaldehyde hydrazone, and 4-quinolinecarboxaldehydehydrazone obtained above with a 1,2,3-tribromopropane to form Compound(14). 3-Formyl-9-ethylcarbazole hydrazone was dissolved in DMSO. Afterthe addition of 25% aqueous solution of NaOH, 1,2,3-tribromopropane wasadded to the solution. The molar ratio of 3-formyl-9-ethylcarbazolehydrazone to 1,2,3-tribromopropane was 1:1. This solution was stirred at70° C. for approximately 1 hour. To this solution was added4-(diphenylamino)-benzaldehyde hydrazone. The molar ratio of4-(diphenylamino)benzaldehyde hydrazone to 1,2,3-tribromopropane was1:1. After the addition was completed, the solution was heated at 70° C.for additional one hour. To this solution was added4-quinolinecarboxaldehyde hydrazone. The molar ratio of4-quinolinecarboxaldehyde hydrazone to 1,2,3-tribromopropane was 1:1.After the addition is completed, the solution was heated at 70° C. foradditional one hour. The product from this reaction was isolated andpurified.

Compound (15)

The first step was the preparation of a 3-formyl-9-ethylcarbazole byVilsmeier reaction. 9-Ethylcarbazole (obtained commercially from AldrichChemical Company, Milwaukee, Wis.) was dissolved in dimethylformamide(DMF) and then the solution is cooled. Phosphorus oxychloride (POCl₃)(10-15% excess) is added slowly via a dropping funnel to the cooled DMFsolution. 3-Formyl-9-ethylcarbazole was isolated and purified.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added3-formyl-9-ethylcarbazole (1 mole, 223 g) and tetrahydrofuran (600 ml).Heating was applied to ensure that all solid entered into solution.Phenyl hydrazine (119 g, 1.1 mole, obtained commercially from AldrichChemical Company, Milwaukee, Wis.) was added and the mixture wasrefluxed for 2 hours. When TLC showed the total disappearance of thestarting material and the formation of the product, the flask wasallowed to cool to room temperature and the solvent was evaporated.3-Formyl-9-ethylcarbazole hydrazone was isolated and purified.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added4-(diphenylamino)benzaldehyde (1 mole, 273 g, commercially obtained fromFluke, Milwaukee, Wis.) and tetrahydrofuran (600 ml). Heating wasapplied to ensure that all solid entered into solution. Phenyl hydrazine(119 g, 1.1 mole, obtained commercially from Aldrich Chemical Company,Milwaukee, Wis.) was added and the mixture was refluxed for 2 hours.When TLC showed the total disappearance of the starting material and theformation of the product, the flask was allowed to cool to roomtemperature and the solvent was evaporated.4-(Diphenylamino)benzaldehyde hydrazone was isolated and purified.

To a 2-liter 3-neck round bottom flask equipped with mechanical stirrerand reflux condenser and heating mantle were added 9-formyl-julolidine(1 mole, 201 g, obtained commercially from Aldrich Chemical Company,Milwaukee, Wis.) and tetrahydrofuran (600 ml). Heating was applied toensure that all solid entered into solution. Phenyl hydrazine (119 g,1.1 mole, obtained commercially from Aldrich Chemical Company,Milwaukee, Wis.) was added and the mixture was refluxed for 2 hours.When TLC showed the total disappearance of the starting material and theformation of the product, the flask was allowed to cool to roomtemperature and the solvent was evaporated. 9-Formyl-julolidinehydrazone was isolated and purified.

The last step was the reaction of 3-formyl-9-ethylcarbazole hydrazone,4-(diphenylamino)benzaldehyde hydrazone, and 9-formyl-julolidinehydrazone obtained above with a 1,2,3-tribromopropane to form Compound(15). 3-Formyl-9-ethylcarbazole hydrazone was dissolved in DMSO. Afterthe addition of 25% aqueous solution of NaOH, 1,2,3-tribromopropane wasadded to the solution. The molar ratio of 3-formyl-9-ethylcarbazolehydrazone to 1,2,3-tribromopropane was 1:1. This solution was stirred at70° C. for approximately 1 hour. To this solution was added4-(diphenylamino)-benzaldehyde hydrazone. The molar ratio of4-(diphenylamino)benzaldehyde hydrazone to 1,2,3-tribromopropane was1:1. After the addition was completed, the solution was heated at 70° C.for additional one hour. To this solution was added 9-formyl-julolidinehydrazone. The molar ratio of 9-formyl-julolidine hydrazone to1,2,3-tribromopropane was 1:1. After the addition is completed, thesolution was heated at 70° C. for additional one hour. The product fromthis reaction was isolated and purified.

G. Investigation of Unexpected Results

Upon investigation of the physical properties of the compounds madeaccording to the practice of the present invention, it was noted mixtureof at least two charge control materials of the invention increased thesolubility of each of the compounds, increasing the concentration ofcharge control material that could be provided in solutions and incoatings. This finding is supported by the following data.

Evaluation of a Mixture of Compound 1 and Compound 2

The following solutions were prepared and did not precipitate when leftovernight in THF (tetrahydrofuran) solvent. A 15% solid and a 20% solidformulation of a 1-to-1 ratio of polycarbonate (CTM:PCZ200), using a50:50 mixture of Compound 1 and Compound 2 (referred to in the Table asCmpd 1,2) for the CTM. Both of these solutions were knife coated on PET(polyethylene terephthalate) using the above described positive chargingIDL construction. The electrostatics were recorded on Hawk Mech andcompared with two other samples of compound 2 of U.S. Pat. No. 6,140,004(referred to in the table as PA) at 15% and 20% solids, as shown in thefollowing table:

TABLE II Prodstart Prodstop Material CA Disch. Contr. DD Res. CA Disch.Cont. DD Res. 15% 492 52 440 38 20 515 61 454 35 30 Cmpd 1,29 20% 484 55429 35 25 538 75 463 34 38 Cmpd 1,2 15% PA 477 38 439 30 11 488 44 44433 14 20% PA 498 67 451 35 21 618 76 542 34 29

In the above Table II: CA is the charge acceptance voltage, the maximumvoltage that the sample can obtain (with the given laser settings) andmeasured by the probe 1.

Disch. Is the discharge voltage obtained after illumination of thecharged photoconductor with light, as measured by the probe 1.

DD is the dark decay measured as the voltage difference between probe 1and probe 2, and is obtained when the charge acceptance voltage ismeasured.

Res. is the residual voltage measured after allowing for one drumrevolution, then exposing the photoconductor to LED (light emittingdiode) light, and measured at probe 1.

Contr. is the contrast of the charge on charged and discharged areas.

The above descriptions and examples are intended to provide a broad andgeneric teaching and enablement of a generic invention. The examplesshould not be read as imposing limits upon the general and generic termsused to describe the practice of the present invention. Generic andspecific embodiments are described within the following claims.

What is claimed is:
 1. A charge transport compound having the followinggeneric formula: (R—Q)n-Y wherein R is selected from the groupconsisting of julolidine ring groups, carbazole ring groups, andtriarylmethane ring group Q comprises an aromatic hydrazone linkinggroup; Y comprises a bridging group between R—Q— groups; and n is aninteger between 2 and
 6. 2. The charge transport compound of claim 1wherein Q comprises an aromatic linking group of the formula:

Z is an aryl group; and X is a linking group.
 3. The charge transportcompound of claim 2 wherein Z is a phenyl group.
 4. The charge transportcompound of claim 2 wherein X is —(CH₂)_(m)—, where m is an integerbetween 0 and
 20. 5. The charge transport compound of claim 2 wherein Xis an alkylene group.
 6. The charge transport agent of claim 5 whereinthe alkylene group is substituted with at least one group selected fromthe group consisting of an alkylene where one or more of methylenegroups in the alkylene is optionally replaced by an oxygen atom, acarbonyl group, urethane, urea, an ester group, a —NR₆ group, a CHR₇group, or a CR₈R₉ group where R₆, R₇, R₈, and R₉ are, independently, H,an alkyl group, or aryl group.
 7. The compound of claim 2 wherein Y is achemical bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, abranched or linear —(CH₂)_(p)— group where p is an integer between 0 and10, an aryl group, a cycloalkyl group, a cyclosiloxyl group, aheterocyclic group, or a CR₁₀ group where R₁₀ is hydrogen atom, an alkylgroup, or aryl group.
 8. The compound of claim 1 wherein Y is a chemicalbond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a branchedor linear —(CH₂)_(p)— group where p is an integer between 0 and 10, anaryl group, a cycloalkyl group, a cyclosiloxyl group, a heterocyclicgroup, or a CR₁₀ group where R₁₀ is hydrogen atom, an alkyl group, oraryl group.
 9. The charge transport compound of claim 1 having thestructural formula:


10. An organic photoreceptor that includes: (a) a charge transportcompound having the formula (R—Q)n-Y  Formula I wherein R is selectedfrom the group consisting of julolidine ring groups, carbazole ringgroups, and triarylmethane ring groups; Q comprises an aromatichydrazone linking group; Y comprises a bridging group between R—Q—groups; n is an integer between 2 and 6, inclusive; (b) a chargegenerating compound; and (c) an electrically conductive substrate. 11.The organic photoreceptor of claim 10 wherein the aromatic hydrazonegroup has the formula:

wherein Ar is an aromatic group, and X is a divalent linking groupselected from a chemical bond, carbon atom, nitrogen atom, oxygen atom,sulfur atom, a branched or linear —(CH₂)_(p)— group where p is aninteger between 0 and 10, an aryl group, a cycloalkyl group, acyclosiloxyl group, a heterocyclic group, and a CR₁₀ group where R₁₀ ishydrogen atom, an alkyl group, or aryl groups.
 12. The organicphotoreceptor of claim 10 wherein the aromatic hydrazone group has theformula:

Z is a phenyl group; and X is a methylene group.
 13. An organicphotoreceptor comprising: (a) a charge transport compound having theformula

where n is an integer between 2 and 6, inclusive; R₁ is hydrogen, abranched or linear alkyl group, a branched or linear unsaturatedhydrocarbon group, an ether group, or an aryl group; R₂ is hydrogen, ahalogen, hydroxy group, thiol group, an alkoxy group, a branched orlinear alkyl group, a branched or linear unsaturated hydrocarbon group,an ether group, a cycloalkyl group, an aryl group, or a —NR₁R₅ groupwhere R₄ and R₅ are, independently, hydrogen, a branched or linear alkylgroup, a branched or linear unsaturated hydrocarbon group, a cycloalkylgroup, an aryl group, or R₄ and R₅ combine with the nitrogen atom toform a ring; R₃ is hydrogen, a halogen, hydroxy group, thiol group, analkoxy group, a branched or linear alkyl group, a branched or linearunsaturated hydrocarbon group, an ether group, a cycloalkyl group, or anaryl group; X is a linking group having the formula —(CH₂)_(m)—,branched or linear, where m is an integer between 0 and 20, inclusive,and one or more of the methylene groups is optionally replaced by anoxygen atom, a carbonyl group, urethane, urea, an ester group, a —NR₆group, a CHR₇ group, or a CR₈R₉ group where R₆, R₇, R₈, and R₉ are,independently, H, an alkyl group, or aryl group; and Y is a bond, carbonatom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear—(CH₂)_(p)— group where p is an integer between 0 and 10, an aryl group,a cycloalkyl group, a cyclosiloxyl group, a heterocyclic group, or aCR₁₀ group where R₁₀ is hydrogen atom, an alkyl group, or aryl group;(b) a charge generating compound; and (c) an electrically conductivesubstrate.
 14. An organic photoreceptor according to claim 13 whereinsaid organic photoreceptor is in the form of a flexible belt.
 15. Anorganic photoreceptor according to claim 13 comprising: (a) a chargetransport layer comprising said charge transport compound and apolymeric binder; (b) a charge generating layer comprising said chargegenerating compound and a polymeric binder; and (c) said electricallyconductive substrate.
 16. An electrophotographic imaging apparatuscomprising: (a) a plurality of support rollers, at least one having adiameter no greater than about 40 mm; and (b) an organic photoreceptorin the form of a flexible belt threaded around said support rollers,said organic photoreceptor comprising: (i) a charge transport compoundhaving the formula

where n is an integer between 2 and 6, inclusive; R₁ is hydrogen, abranched or linear alkyl group, a branched or linear unsaturatedhydrocarbon group, an ether group, or an aryl group; R₂ is hydrogen, ahalogen, hydroxy group, thiol group, an alkoxy group, a branched orlinear alkyl group, a branched or linear unsaturated hydrocarbon group,an ether group, a cycloalkyl group, an aryl group, or a —NR₄R₅ groupwhere R₄ and R₅ are, independently, hydrogen, a branched or linear alkylgroup, a branched or linear unsaturated hydrocarbon group, a cycloalkylgroup, an aryl group, or R₄ and R₅ combine with the nitrogen atom toform a ring; R₃ is hydrogen, a halogen, hydroxy group, thiol group, analkoxy group, a branched or linear alkyl group, a branched or linearunsaturated hydrocarbon group, an ether group, a cycloalkyl group, or anaryl group; X is a linking group having the formula —(CH₂)_(m)—,branched or linear, where m is an integer between 0 and 20, inclusive,and one or more of the methylene groups is optionally replaced by anoxygen atom, a carbonyl group, urethane, urea, an ester group, a —NR₆group, a CHR₇ group, or a CR₈R₉ group where R₆, R₇, R₈, and R₉ are,independently, H, an alkyl group, or aryl group; and Y is a bond, carbonatom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear—(CH₂)_(p)— group where p is an integer between 0 and 10, an aryl group,a cycloalkyl group, a cyclosiloxyl group, a heterocyclic group, or aCR₁₀ group where R₁₀ is hydrogen atom, an alkyl group, or aryl group;(ii) a charge generating compound; and (iii) an electrically conductivesubstrate.
 17. An electrophotographic imaging apparatus according toclaim 16 wherein said charge transport compound has the formula


18. An electrophotographic imaging process comprising: (a) applying anelectrical charge to a surface of an organic photoreceptor comprising:(i) a charge transport compound having the formula

where n is an integer between 2 and 6, inclusive; R₁ is hydrogen, abranched or linear alkyl group, a branched or linear unsaturatedhydrocarbon group, an ether group, or an aryl group; R₂ is hydrogen, ahalogen, hydroxy group, thiol group, an alkoxy group, a branched orlinear alkyl group, a branched or linear unsaturated hydrocarbon group,an ether group, a cycloalkyl group, an aryl group, or a —NR₄R₅ groupwhere R₄ and R₅ are, independently, hydrogen, a branched or linear alkylgroup, a branched or linear unsaturated hydrocarbon group, a cycloalkylgroup, an aryl group, or R₄ and R₅ combine with the nitrogen atom toform a ring; R₃ is hydrogen, a halogen, hydroxy group, thiol group, analkoxy group, a branched or linear alkyl group, a branched or linearunsaturated hydrocarbon group, an ether group, a cycloalkyl group, or anaryl group; X is a linking group having the formula —(CH₂)_(m)—,branched or linear, where m is an integer between 0 and 20, inclusive,and one or more of the methylene groups is optionally replaced by anoxygen atom, a carbonyl group, urethane, urea, an ester group, a —NR₆group, a CR₇ group, or a CR₈R₉ group where R_(6 , R) ₇, R₈, and R₉ are,independently, H, an alkyl group, or aryl group; and Y is a bond, carbonatom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear—(CH₂)_(p)— group where p is an integer between 0 and 10, an aryl group,a cycloalkyl group, a cyclosiloxyl group, a heterocyclic group, or aCR₁₀ group where R₁₀ is hydrogen atom, an alkyl group, or aryl group;(ii) a charge generating compound; and (iii) an electrically conductivesubstrate; (b) imagewise exposing said surface of said organicphotoreceptor to radiation to dissipate charge in selected areas andthereby form a pattern of charged and uncharged areas on said surface;(c) contacting said surface with a liquid toner comprising a dispersionof colorant particles in an organic liquid to create a toned image; and(d) transferring said toned image to a substrate.
 19. Anelectrophotographic imaging process according to claim 18 wherein saidcharge transport compound has the formula


20. A charge transport compound having the formula

where n is an integer between 2 and 6, inclusive; R₁ is hydrogen, abranched or linear alkyl group, a branched or linear unsaturatedhydrocarbon group, an ether group, or an aryl group; R₂ is hydrogen, ahalogen, hydroxy group, thiol group, an alkoxy group, a branched orlinear alkyl group, a branched or linear unsaturated hydrocarbon group,an ether group, a cycloalkyl group, an aryl group, or a —NR₄R₅ groupwhere R₄ and R₅ are, independently, hydrogen, a branched or linear alkylgroup, a branched or linear unsaturated hydrocarbon group, a cycloalkylgroup, an aryl group, or R₄ and R₅ combine with the nitrogen atom toform a ring; R₃ is hydrogen, a halogen, hydroxy group, thiol group, analkoxy group, a branched or linear alkyl group, a branched or linearunsaturated hydrocarbon group, an ether group, a cycloalkyl group, or anaryl group; X is a linking group having the formula —(CH₂)_(m)—,branched or linear, where m is an integer between 0 and 20, inclusive,and one or more of the methylene groups is optionally replaced by anoxygen atom, a carbonyl group, urethane, urea, an ester group, a —NR₆group, a CHR₇ group, or a CR₈R₉ group where R₆, R₇, R₈, and R₉ are,independently, H, an alkyl group, or aryl group; and Y is a bond, carbonatom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear—(CH₂)_(p)— group where p is an integer between 0 and 10, an aryl group,a cycloalkyl group, a cyclosiloxyl group, a heterocyclic group, or aCR₁₀ group where R₁₀ is hydrogen atom, an alkyl group, or aryl group.21. A charge transport compound having the formula:

R₁, R₂, and R₃ are, independently, a branched or linear alkyl group, abranched or linear unsaturated hydrocarbon group, a cycloalkyl group, aheterocyclic group, or an aryl group; R₄, R₅, and R₆ are, independently,triarylamine, diaryl alkylamine, dialkyl arylamine, a carbocyclic ring,or a heterocyclic ring group; and X is a linking group having theformula

where m, n, and o are independently an integer between 0 and 50,inclusive; one or more of the methylene groups is optionally replaced bya bond, an oxygen atom, a sulfur atom, a carbonyl group, an urethanegroup, an urea group, an ester group, an aryl group, a heterocyclicgroup, a NR₅ group, a CHR₆ group, or a CR₇R₈ group where R₅, R₆, R₇, andR₈ are, independently, H, an alkyl group, or an aryl group; and the C—Hgroup is optionally replaced by a nitrogen atom, a boron atom, a metalatom, and a CR₉ group where R₉ is an alkyl group or an aryl group. 22.The charge transport compound of claim 21 wherein R₁, R₂, and R₃ are,independently selected from julolidine, carbazole and triarylmethanegroups.
 23. The charge transport compound of claim 21 wherein R₁, R₂,and R₃ are all either julolidine, carbazole or triarylmethane groups.